You'll have to decide when and how to round. Keeping individual billing items at high precision and rounding after summing them up can work; defining and documenting a rounding policy (or complying with whatever's legally required in your jurisdiction/domain) and rounding each individual billed item can as well.

You use 1/1000th or 1/10000th or whatever you need. You do not need “cents”.

Currency: USD Amount: 99500 Decimals: 5

Round it up