If you live in a world of penny profit the way grocers do, you can't afford to discount to people willing to pay full price. You also need to drive in footsteps to buy product that is literally perishable.
So where does that leave you?
Needing to promote the right products to the right customers at the right time based on what they've bought historically, what they're likely to buy now, and what are your most profitable products based on fluctuating manufacturer subsidies....