Hi Camila,
I agree with Rajesh.
I would use a mix of ABAP development & adhoc SIS infostructure based on the sales group to get summarized amounts & speed up the Commission Reporting Process.
You will have to consider if comisions are paid depending on sold amounts or invoiced amounts.
I guess sold amounts in your case, that's pretty obvious the sales person does not want to wait 5 years for bridge to be built to get his commision check Image may be NSFW.
Clik here to view.
Important: When rejecting a sales order item, there is a customizing switch in the reason for rejection so you can decide not to update statistics for rejected sales orders / sales items. This is important because on the contrary the Sales Person would get twice the commission!!
Best Regards,
Franck