I'd go as far as to say that any value which may be displayed to the user should almost always be an integer. Money is only the most prominent example of this. Dealing 225 damage four times to a monster with 900 HP and finding that it still has 1 HP left will subtract from the experience just as much as finding that you are an invisible fraction of a penny short of affording something.
On the more technical side I think it's worth noting that one doesn't have to revert to floats to do advanced stuff like interest. As long as you have got enough headroom in your chosen integer type a multiplication and a division will stand in for a multiplication by a decimal number, for instance to add 4%, rounded down:
number=(number*104)/100
To add 4%, rounded by standard conventions:
number=(number*104+50)/100
No float point inaccuracy here, the rounding always split exactly on the .5 mark.