Unless you are moving away and never plan to work in retail or shop at stores anymore, it will probably come back to bite you. Even if you think it won't, you might be surprised.
I worked at Target while I was in school. When I finished my MBA and took a corporate job, they didn't take me off the schedule in time to avoid conflict with the start date of my new "real" job. I was tempted to just let Target deal with it since I had told them before the schedule was posted, and I was moving on to bigger and better things.
When I came back to work at the same Target after losing my job last year, so that my family could afford to have a modest Christmas instead of nothing at all, I was really glad I handled my departure professionally and didn't abandon my job all those years ago.
You will never regret doing the right thing.