pricing as per income tax slabs

We have a following scenario:

Example Sum total of quantity range on the order = 0-100 for price 5.00, 101-500 for price 4.00, 501-1000 for price of 3.00 and so onLine #   Quantity    Expected Price=============================1             50                5.00           ---------- Because at this line the sum total of quantity on the order is between 0-1002             25                5.00           ---------- Because at this line the sum total of quantity on the order is between 0-1003             25                5.00           ---------- Because at this line the sum total of quantity on the order is between 0-1004             40                4.00           ---------- Because at this line the sum total of quantity on the order is between 101-5005           300                4.00