I can't seem to find anything on what I need to do. Maybe one of you guys can help.

I'm looking for a module that will enable me to calculate a commission or royalty to a referrer (charity) based on the value of the customer's purchase on checkout.

I guess any sort of referral tracking mechanism that would enable a user to select predefined referrers from a check list or drop box would suit this purpose, or another way would be to have a standardized "common" code (like 'ASPCA') to generate a report so that I can direct the proceeds later.

Thanks!