Diagnose & fix issue with shopping cart sending info to paypal

I have a site built on wordpress using the shopperpress cart. When multiple items are added to the cart the shopperpress cart calculates the tax just fine but then when you click pay now and go to paypal the tax is removed. Also for some reason with a single item the tax shows up on paypal just fine. Please only bid if you can begin work on this right away & please bid showing your wordpress experience