I want offer a volume discount on sub-groups of products within the products sold on my website.

As an example, let's say we sell five types of savories A, B, C, D, and E. Is there a way to define A, B, and C as a a group and then offer a discount on that group if the customers buys more than 3 of them?

If that's not possible, is it possible to do it a the level of product categories? ie. A B and C are in a product category and buying more than 3 kicks in a discount on those products.

Any ideas or suggestions would be very much appreciated.

Andrew