No, it's just that we're in the realm of predictions and modelling, not accounting. If you're constructing a curve to forecast 50 years of interest rates from a

No, it's just that we're in the realm of predictions and modelling, not accounting. If you're constructing a curve to forecast 50 years of interest rates from a limited set of instruments, you're already accepting a margin of error orders of magnitude greater than the inaccuracies introduced by floating point. The models also use transcendental functions which cannot be accurately calculated with fixed point, rationals, integers etc.