Samsung ER-4940 tax programming help?

At our business we are using a several-years-old Samsung ER-4940 cash register. For within-state mail order sales here in WA state, we will soon need to start collecting sales tax based on the tax rate at the ship-to destination. This means that we will need the capability to calculate sales tax at many different rates. My understanding of the ER-4940 is that it is designed to handle up to 3 tax rates. Is there a way to progam this register to bypass this limitation such that the appropriate tax rate (in %; or even a pre-calculated tax amount) can be manually entered in order to handle many different tax rates? If so, how? Any help would be appreciated?