Simple price break for bulk orders

-- url of the page with the problem -- : amarillosnuff.com/index.php/products
-- Joomla version -- : 3.7.2

Why can I set up a simple bulk rate for multiples of the same product, but not for multiple products? That makes no sense. Every product costs $4.5 unless they buy 5 or more, and then the cost falls to $4. EVERY. PRODUCT. Not just five of each product. One of each of five products. Why is this so difficult to force this system to do? There has to be an easy way that DOES NOT involve having the customers input a coupon. It needs to happen seamlessly and invisibly in the background. If a customer (as happened today) orders four of one, one of another, and one of a third, they should cost $4 each. Instead, he was charged $4.50 each.

How do I make that happen? It's frustrating to my client and to the customers.