My website sells prints of art in custom sizes. Because of this, I need the flexibility to allow customers to enter an order quantity that is not a whole number, as orders are being placed in square feet, based on the size of the original picture.
This means that if a customer would like to order a print of a picture, that is 3.75 square feet in size (18" tall by 30" wide), my cart needs to be able to accept an order quantity of 3.75. As a natural extension of this requirement, the math done by the shopping cart, must also be correct.
Currently, if I enter an order quantity of 3.75, the shopping cart automatically enters an order quantity of 3 and then bases the cost per unit on the cost of 3 square feet, instead of 3.75 square feet.