Round tax amount instead of ceil

lib/recurly/pricing/checkout/calculations.js

@@ -4,7 +4,7 @@ import Promise from 'promise';
 import uniq from 'array-unique';
 import decimalizeMember from '../../../util/decimalize-member';
 import groupBy from '../../../util/group-by';
-import taxCeil from '../../../util/tax-ceil';
+import taxRound from '../../../util/tax-round';
 
 /**
  * Checkout pricing calculation handler
@@ -184,8 +184,8 @@ export default class Calculations {
 
     // If tax amount has been specified, simply apply it
     if (this.items.tax && this.items.tax.amount) {
-      this.price.now.taxes = taxCeil(this.items.tax.amount.now);
-      this.price.next.taxes = taxCeil(this.items.tax.amount.next);
+      this.price.now.taxes = taxRound(this.items.tax.amount.now);
+      this.price.next.taxes = taxRound(this.items.tax.amount.next);
       return Promise.resolve();
     }
 
@@ -232,8 +232,8 @@ export default class Calculations {
           return taxRates.indexOf(taxRate) === i;
         }).map(JSON.parse);
         this.price.taxes = taxRates;
-        this.price.now.taxes = taxCeil(taxNow);
-        this.price.next.taxes = taxCeil(taxNext);
+        this.price.now.taxes = taxRound(taxNow);
+        this.price.next.taxes = taxRound(taxNext);
       });
   }
 

lib/recurly/pricing/subscription/calculations.js

@@ -2,7 +2,7 @@ import each from 'component-each';
 import find from 'component-find';
 import isEmpty from 'lodash.isempty';
 import decimalizeMember from '../../../util/decimalize-member';
-import taxCeil from '../../../util/tax-ceil';
+import taxRound from '../../../util/tax-round';
 
 /**
  * Subscription pricing calculation handler
@@ -94,8 +94,8 @@ export default class Calculations {
 
     // If tax amount has been specified, simply apply it
     if (this.items.tax && this.items.tax.amount) {
-      this.price.now.tax = taxCeil(this.items.tax.amount.now);
-      this.price.next.tax = taxCeil(this.items.tax.amount.next);
+      this.price.now.tax = taxRound(this.items.tax.amount.now);
+      this.price.next.tax = taxRound(this.items.tax.amount.next);
       return done.call(this);
     }
 
@@ -118,9 +118,9 @@ export default class Calculations {
             this.price.taxes.push(tax);
           });
 
-          // tax estimation prefers partial cents to always round up
-          this.price.now.tax = taxCeil(this.price.now.tax);
-          this.price.next.tax = taxCeil(this.price.next.tax);
+          // tax estimation prefers partial cents to round to the nearest cent
+          this.price.now.tax = taxRound(this.price.now.tax);
+          this.price.next.tax = taxRound(this.price.next.tax);
         }
         done.call(this);
       });

lib/util/tax-round.js

@@ -0,0 +1,14 @@
+/**
+ * Round the second decimal of a number without risk of
+ * floating point math errors
+ *
+ * - returns zero if the result is negative
+ *
+ * @param {Number} number
+ * @return {Number}
+ */
+
+export default function taxRound (number) {
+  number = Math.max(number, 0);
+  return +((number < 0 ? -1 : 1) * Math.round(Math.abs(number) + 'e+2') + 'e-2');
+}

test/unit/pricing/checkout/checkout.test.js

@@ -1589,8 +1589,8 @@ describe('CheckoutPricing', function () {
         it('applies taxes to the price', function (done) {
           this.pricing.reprice().done(price => {
             assert.equal(price.now.subtotal, 61.99); // 21.99 + 20 + 20
-            assert.equal(price.now.taxes, 5.43); // 8.75% of 61.99
-            assert.equal(price.now.total, 67.42);
+            assert.equal(price.now.taxes, 5.42); // 8.75% of 61.99
+            assert.equal(price.now.total, 67.41);
             assert.equal(price.next.subtotal, 19.99);
             assert.equal(price.next.taxes, 1.75); // 8.75% of 19.99
             assert.equal(price.next.total, 21.74);

test/unit/pricing/subscription/subscription.test.js

@@ -46,7 +46,7 @@ describe('Recurly.Pricing.Subscription', function () {
         })
         .giftcard("hundred-dollar-card")
         .done(function (price) {
-          assert.equal(price.now.gift_card, '23.92');
+          assert.equal(price.now.gift_card, '23.91');
           assert.equal(price.next.gift_card, '21.74');
           assert.equal(price.now.total, '0.00');
           assert.equal(price.next.total, '0.00');
@@ -65,7 +65,7 @@ describe('Recurly.Pricing.Subscription', function () {
           assert.equal(price.taxes.length, 1);
           assert.equal(price.taxes[0].type, 'us');
           assert.equal(price.taxes[0].rate, '0.0875');
-          assert.equal(price.now.tax, '1.93');
+          assert.equal(price.now.tax, '1.92');
           assert.equal(price.next.tax, '1.75');
           done();
         });
@@ -99,7 +99,7 @@ describe('Recurly.Pricing.Subscription', function () {
           assert.equal(price.taxes[0].type, 'us');
           assert.equal(price.taxes[0].rate, '0.0875');
           assert.equal(price.taxes[0].region, 'CA');
-          assert.equal(price.now.tax, '1.93');
+          assert.equal(price.now.tax, '1.92');
           assert.equal(price.next.tax, '1.75');
           done();
         });
@@ -151,7 +151,7 @@ describe('Recurly.Pricing.Subscription', function () {
             assert.equal(price.taxes.length, 1);
             assert.equal(price.taxes[0].type, 'us');
             assert.equal(price.taxes[0].rate, '0.0875');
-            assert.equal(price.now.tax, '1.93');
+            assert.equal(price.now.tax, '1.92');
             assert.equal(price.next.tax, '1.75');
             done();
           });
@@ -172,7 +172,7 @@ describe('Recurly.Pricing.Subscription', function () {
             assert.equal(price.taxes.length, 1);
             assert.equal(price.taxes[0].type, 'us');
             assert.equal(price.taxes[0].rate, '0.0875');
-            assert.equal(price.now.tax, '1.93');
+            assert.equal(price.now.tax, '1.92');
             assert.equal(price.next.tax, '1.75');
             done();
           });