discount on cart total for Virtuemart.

This project is for a Virtuemart 2.26d shop. I want to give a shopper discount based on the cart total with the option to create ranges with different discounts, eg cart-total > 1.000 - 5% discount, cart-total > 2.000 - 10% discount. cart-total >10.000 - 15% discount. The discount should be visible in the confirmation mail, back-end, etc. Preferably, I would like it in a plugin without changes in the Virtuemart installation. (templates overrides are not a problem of course)