I am in the process of setting up Zen Cart to use with PayPal. I have only one product and one price which includes shipping but not sales tax. I am currently using PayPal, however, if you set it up with Auto Return 'ON' and PayPal 'OPTIONAL' the purchaser will not automatically be returned to the 'Thank You' page. I need to have this happen unconditionally for reasons of tracking sales. If anyone has been down this road before I'd like to hear how you set it up.