The module adds a new product attribute in the 'General' tab, called 'Multiples Of X' - default set to 1. For example, set it to 5. This forces products to be ordered in quantities of 5, 10, 15. A warning message is shown if it isn't. Shows (+) and (-) buttons next to the quantity box on the product page.
Note: the lowest possible Multiples Of X will act as a Minimal Qty. For example, if your Multiples Of X = 5, but your Minimum Qty = 2, then of course "2" can never be ordered, because "2" is not a multiple of "5". And thus acts like a minimal quantity, forcing you to order at least "5".