[Plugin: WP e-Commerce] Add groups of items to cart

Hi There.
I’m guess if it’s possible to add different group of items to cart. For exemple: i want that my visitors choose to buy 1 – 20 – 50 or 100 pieces of the same product, with a discount percentage on big quantities.

Here is an exemple : http://www.pubblicarrello.com/uomo-tshirt-manica-corta

Thanks.
Giulio

http://wordpress.org/extend/plugins/wp-e-commerce/