Quantity discounts across products.

How can I set up a cart to offer quantity discounts for several different but similar products? For example; say I am selling audio cassettes, cds, and dvds all with different titles and product descriptions. If a user purchases 10 cds with different titles I would like to provide a discount. Likewise with the cassettes and dvds with several price breaks. Is there a way to do this with the existing cart?

Use the Quantity Discounts contribution.

Thanks for the reply. My quantity pricing is further complicated since I will be offering multiple piece packages. So the customer will be able to purchace a single item, a package of 5, a package of 10, or a discount on 10 packages of 10. I would like the customer to be able to buy 5 packages of product A and 5 packages product B and get the bulk price for the combined order, yet I still want to offer the smaller package for the same product at the small package price. It appears that Quantity Discount contribution would require all package sizes to be the same price for the same product. Is this correct?

After reviewing the documenation I think that the quantity discounts contribution may do the trick. If I modify the code in apply_special_category_discount() for the categories I want to be discounted, will the admin settings for order_total->quantitiy discounts be overridden (i.e. can I ignore them)?

You can use this or the other category related user exit, exclude_category, depending on your needs.