This method does not work because I have four different discount schedules.
I have added a price code to each item when added to the cart, which will determine the discount schedule to be used for that particular item.
e.g.
1mm sterile short has a base price of $16.00 and it's discount schedule code is 1
1.5mm sterile short has a base price of $16.00 and it's discount schedule code is 1
1mm sterile long has a base price of $17.00 and it's discount schedule code is 2
1.75mm sterile long has a base price of $17.00 and it's discount schedule code is 2
The break points are the same, but the discount amounts vary based on the drill type and it's price code.