Automatic redirect back to merchant store and/or implementation questoin

I would like for the customer to be redirected back to my
store
automatically after completing checkout.  This is a
configuration
setting with Paypal, which can redirect on final page after
10 seconds.
 I am having issues with my cart, Interchange, as to if I
should close
the cart before GC (then they can't go back when entering
GC) or after
(but if they don't click 'continue, I have problem). My GC
message
server can not communicate with the shoopers cart to close
upon receipt
of new-order-notification message.
thank you for suggestions,
tom friedel
tomreadyink.com
http://www.readyink.com