In a simulation nobody is calculating n x m^k. They’re calculating n X m in k loops spread over k ticks. And given that fact, if you round or truncate at the end of each cycle, as one often does with game points (eg, fire resistance in D&D), then there is no problem.

For money systems, we also tend to round on every step to the nearest penny.

What you don’t have with rationals is the problem of 10.00 - 4.10 + 3.20 ending in a 9.