Fix tax class/rate in OSCommerce

I have a OSCommerce store that I need the tax class/rate section to work correctly. When I assign a tax class to an individual product it charges the tax to all customers who order/view the product. Since sales tax is only charged to residents of that particular state, I need it to show the correct tax rate if you reside in that state. All other customers should show a price without tax. Maybe I am not understanding how to apply this correctly. I am new to sales tax stuff. Also some of the headers in the admin section (Locations/Tax) are missing.