Rebate Scenario

I have a business scenario related to rebate, wherein i will give rebate to the customer if he order 200 units of a item before 10th of every month, also as per my company policy we are fileing the Tax on the 8th of every month, now say if the customer has order 190 items till 8th, i will submit my Tax accordingly, but if he orders 20 more items on the 9th, obviously i will give him the rebate but my Tax submission will deviate and adjustments of that in the future are tiresome & conflicting. is there a way to overcome or mitigate the issue in SAP?

Please help