osCommerce Discount Preview allows your customers to see their order total discounts on the shopping cart page. Without Discount Preview, they won't be visible until the Order Confirmation page. It is designed to work in conjunction with my Better Together and Quantity Discounts contributions, as well as Discount Chooser for osCommerce (formerly Free Gift Chooser).
You may preview whatever combinations of these discounts is configured for your shop.
For more information, please visit this product's webpage.