Used to work at a payments company. Yes, you need to be *very* explicit in how you model currency amounts and precision. See also earlier post about Canadian rounding rules. Some of the "logic" is regulatory/compliance driven.

ref child post about stocks trading for 0.0001. Yes, those are real trades and (probably) fully legal etc, but I'm not sure the Fed recognizes currency amounts less than 1 US cent ($0.01), so the accounting rules and tax rules might not match expectations based on generalized floating point math.