It sounds like you primarily use Offers as your method of discounting since these apply at the order/cart level. Have you tried creating a Sale? These apply at the product level before it is added to the cart (i.e. you'll see the sale price on category and product pages).

Tiered promotions are typically done on the order, not the product. Consequently, there isn't a simple mechanism for doing this like there is with Offers. It can still be done, however. You will need to setup dynamic categories for each price tier, and then setup a Sale by category for each of those categories. Note that you can hide these dynamic categories so they are not shown in the navigation.