Store sales tax as the rate could change if you need to go back a year from now and reprint.

>I have always been of the opinion that invoice totals should be calculated when needed rather then stored. The problem is that I get a different result, the so called penny difference, when comparing different types of reports.
>When I review others code I see most people are storing the invoice total and sales tax total and using those totals on reports.
>Any ideas as to what the best approach might be?