Generating a BOM from Altium, you can output the purchase quantity, which includes extra quantity to reach the next price break if it's cheaper. Or you can write a rather tedious Excel expression to do this from the Supplier Pricing field. Which also works (with some changes) if you're building the BOM by hand, copy-pasting the raw supplier data.
Occasionally, suppliers themselves will ask if you want to bump an item to the next price break, because it's easier (cheaper) for them, too.
Tim