Make it possible to apply a discount to groups of products in the cart, based on division by a specific number. Example: A "buy 3 for $250" deal where: * If you have 3 in the cart: you pay $250 * 6 in the cart: $500 * 9 in the cart: $750 * Etc. In addition, it will be smart enough to leave the remainder of items at normal price. For example, if you had 5 in the cart, you'd get $3 of them at $250, but the remaining 2 would be full price. This is different from volume discounts, which can only have a finite number of quantity breaks.
