Tax and shipping estimation is one of the features most commonly asked for by shoppers on Google Product Search (formerly Froogle). “We'll soon be displaying this information on Google Product Search to provide buyers with more accurate price information, so we strongly encourage all merchants to start submitting it.” Google Product Search now, added an option to restrict the results to sellers that offer free shipping. If you enter your location, the service also shows tax and shipping information for some of the products.

More info: Google Base Blog