This can be done for sure.  I would use a Sage Intelligence report. You would need to place a 'factor' in a custom field for each item record.  The Intelligence report could then do calculations on that factor for a commission amount.

This would work if there was a standard commission by item.  However, each Sales Rep has a different commission rate.

It has been quite some time, but I wrote a commission report like that.  Have to place a factor in each Item record & a factor in each Employee record