Credit Rebates to Customers

We are running a program were the customer at the end of the month receives a rebate on how many systems they sell. We have been putting this in as a credit on the customers account. Now that we have a fair amount of customers on this program we have notices that our taxes are off. Should they be put in with the taxes assigned from their county, or should they go in tax exempt? This has thrown off our financials, plus I do not want to get in trouble for not paying the correct amount of taxes.