Tony: I have encountered a similar rounding issue in using the Invoices database to create a Crystal report; in my case, it was in calculating the taxes.

As best I can tell, it appears Invoices calculates each line item and displays the calculation result(s) rounded to 2 decimals. However it retains the amounts to four decimals and uses those in calculating the total(s).

I think your idea of "pre-rounding" before the amounts get into Invoices may be a good way to go.