fix CEILING behavior for values of "significance" that are not powers…

[patriciali]

… of 10

previously, the implementation of CEILING would return 0.3 for CEILING(0.19, 0.25), and 0.8 for CEILING(0.69, 0.25), due to the rounding logic, which doesn't work when significance is not a power of 10.

Google Sheets's implementation does this correctly, and even calls it out explicitly that they handle this:

CEILING is most often used with factor set to a 'round' number such as 0.1 or 0.01 in order to round to a particular decimal place. However, factor can, in fact, be any number of the same sign as value, e.g. CEILING(23.25,0.18) which results in 23.4, which is 0.18 * 130. This can be used, for instance, to round up to a particular denomination of currency (e.g. 0.25 or 0.05 USD).

(see https://support.google.com/docs/answer/3093471?hl=en)