1. A method of discounting products during a retail transaction comprising: a) at a server system, transmitting a first list of promoted products to a retail store system, the first list of promoted products containing product identifiers for the promoted products and, for at least two products, a common group identifier; wherein a first set of products have product identifiers that are associated with the common group identifier, and wherein a second set of products have product identifiers that are not associated with the common group identifier; b) at the server system, receiving from the retail store system a filtered list of products being purchased in a single transaction at the retail store system that are filtered against the first list of promoted products, wherein the single transaction includes products from the first set of products and from the second set of products, further wherein the filtered list of products includes an aggregated total for products purchased from the first set of products without identifying every product identifier for products purchased from the first set of products; further wherein the filtered list of products separately lists every product identifier for products purchased from the second set of products; c) at the server system, calculating an aggregated discount for the first set of products reported in the filtered list of products, and separately calculating a discount for each product in the second set of products reported in the filtered list of products; and d) at the server system, transmitting the calculated aggregated discount and the separately calculated discounts to the retail store system.