Numbers > 0.50 should round up

In your spec, have this expected to be '$1,234,567,890':

   NumberHelpers.number_to_currency(1234567890.506, {precision: 0});

Rails does this (IMO more sensible rounding):

    > number_to_currency(1234567890.506, precision: 0)
      => "$1,234,567,891"

Now, the rounding of .50 up or down is a matter of opinion, but this
is certainly a bug:

   NumberHelpers.number_to_currency(2.999, {precision: 2});

   => $2.00

And even this:

   NumberHelpers.number_to_currency(2.99, {precision: 0});

   => $2

This adds more specs and fixes the bug
Merge pull request #3 from scpike/number-to-currency-rounding-bug

Numbers > 0.50 should round up