Largely due to inertia, consumer psychology where lower sticker prices encourage more purchases even when consumers know the checkout price will be higher, and

Largely due to inertia, consumer psychology where lower sticker prices encourage more purchases even when consumers know the checkout price will be higher, and the fact that taxes can be different based on the type of item you are buying and the exact jurisdiction you are buying it. Two identical stores across the street from each other can have different tax rates if they are in different tax jurisdictions. The stores have the info to calculate this, and do at checkout, so it's really the first two points mostly.