To be fair, higher precision in intermediate calculations in complex equations can in fact cause errors rather than solving them.

I'm certainly no authority on currency laws, so I can't speak to that.

But, from a mathematics standpoint, suppose all intermediate results are supposed to be rounded to 4 decimal places, but instead you carry them out further, say to 8 places. You've changed the intermediate results, which with large multiples of iteration -- such as for interest calculations, etc. -- could change the final result from what it would have been with different rounding of intermediate calcs.