Set a strict grocery budget, and take a list to the store. Each time you get your item, cross it off, round up, and put that number next to that item. ($2.88= 3 on your list) . At the end, add it up. If you are over, reevaluate what you have and if anything can be put back. Don't count coupons either, just use them! At the end your total will probably be less than your budget, and you will have what you Need!
I've done this since my husband and I were eating hot dogs and mac n cheese for dinners. Now, I use the difference and money saved by coupons to put in a savings account for vacations. It becomes a challenge to see what I can save!