I figured out how to get a percentage of two summarized fields and it works perfectly (with one exception). The formula is:
Sum ({@Payments}, {TABLE_NAME}) / Sum ({@Charges}, {TABLE_NAME}) * 100
The report runs fine but if I use the last page arrow key and go to the last page (and everything is still fine) then I hit the one page back arrow button, I get a msg "Division by Zero" and it opens up the formula with everything but the *100 highlighted. Yes, there are some charges that are zero but I can't have them breaking the report like this, what can I do? Thanks

that works perfectly, thank you!