I've been using a small spreadsheet to add up cash on hand for depositing. It would be a great tool to add to gnucash. My spreadsheet consists of 6 lines: $50, $20, $10, $5, $1, coin. I enter the quantity of each and the spreadsheet provides a total. So for example, I have 17 $20 bills ($340), 16 $10 bills ($160), 19 $5 bills ($95), and 66 $1 bills ($66) = $662.

It could be expanded to include $100, or individual coin amounts .25, .10, .05, etc. (I just don't deal with change often).