Forms Data Controls :: Insert Row At Bottom Of Each Section?

I am just getting back into asp.net programming and have gotten stuck on something I suspect is probably not too hard to fix but I can't seem to figure it out. I have a gridview which works fine and have added in subheaders to divide up the content as it's sorted by currency. But I need to insert a row at the bottom of each section that gives a balance determined from a seperate query. Initially I used the same logic as the header so when a currency changed it would insert a total row which works fine except it doesn't do a total row for the last section. I tried using if (e.Row.RowIndex = transactionData.Rows.Count) to determine the last row but those are the same throughout so it puts a total row under every row. Is the problem that I'm trying to do this inside RowDataBound? All I think I need to do is be able to tell when the current gridview row is the last one and then insert a row at the bottom. The code I already have puts in the other total rows.