That trick will not work in my scenario, the store owner wants to send 4 bottles with total of $380 and he wants to increase the total to $400 when fulfilling the order to cover the delivery costs. With your solution he will have to add more bottles then drop the price. He is advertising free delivery but he is technically covering the $20 delivery cost. 380 + 20 = 400
With your approach he will have to add more bottles to pass the $400 then apply a discount.