You can download your Transaction Log to a tab-delimited text file, which you can open in any spreadsheet program (e.g. Excel) to perform whatever calculations you wish from there:
http://www.e-junkie.com/ej/help.transaction-log.htm
The Transaction Log screen also shows a basic summary of Number of Transactions, Number of Items Sold, and total Sale Amount for the transactions listed in that log view. If you select a different date range, specific product, and/or specific affiliate, then click View Log, the summary will show totals for those log view parameters.
Your payment processor account (e.g. PayPal History) may have other built-in methods to analyze your payments as well.
