Adding a quantity discount from a supplier to an item in Item Maintenance (NOT Price)

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I have found many ways to add a price break from the sales standpoint, using Price Codes to adjust the retail price based on ranges of quantities sold to customer. However, I have found very little on how to enter the same info on the Purchases side - I get a price break from my supplier if I order more than X, discounting our cost to manufacture. I want to be able to enter those values so Sage Purchase Order will recognize and populate the correct price based on the quantity ordered. Is there a drop-down menu that I'm missing?