What do the percentage amounts associated with the various retailer gift cards mean?

Those percentages are the rebate amounts that the retailer has agreed to discount to the Gene Grawe Fund. Basically, if a merchant has agreed to a 10% rebate, then the Gene Grawe Fund only pays that merchant $90 for a $100 gift card. The GGF then sells that gift card to someone for the full $100 thereby securing a $10 rebate that will be used to help fund the tuition awards.