VERY small OSCommerce contribution modification

I am currently using Customer Loyalty for an OScommerce store. The contribution is installed fine, but I need to modify it's purpose a little bit. Below are the discount amounts (changed in case anyone finds this) discount, purchase amount MSRP - 5% 0 MSRP - 10% 1500 msrp - 15% 3000 Right now the order totals are calculated this way If someone makes a $1450 purchase, then makes a $50 purchase they can't get the 10% discount. Because the first purchase is stored as $1377 dollars, the discounted price. Purchase discounts should be gauged on previous purchases at MSRP (not discounted) and include the current purchase before discount. So someone who has purchased $1450 at msrp should be able to purchase $50 in product and then qualify for 10% from then out. I will provide the one PHP file. If you need to make a new database table for the modification I will provide login details. I don't believe this should take more than an hour for someone who knows what they're doing. Budget for this mod is under $50.