There seems to be a bug with the Category Quantity Discounts.
To recreate:
If I have 2 different products in two different categories, with 2 different quantity break discounts, the quantities are added together in the cart, giving wrong sales values.
For example:
I have product 1, with a price of $2.00. At a quantity of 25+, it drops to $1.04 each.
I have product 2, with a price of $2.69. At a quantity of 25+, it drops to $1.99 each.
If I add 20 of product 1, and another 5 of product 2, it discounts all the lines to $1.99 (incorrect).