Although I have worked as a checker, I have not worked stocking in a grocery store. I have worked stocking in a toy store, a book store, and two department stores. The managers say they want accurate work. Here's the tricky part:
They want fast work.
They say they want accurate work because some people are so sloppy, plus it kind of protects them if a mistake was made. . .
But they actually want fast work.
So, give them fast. Do good. Work at that good fast clip where you're reasonable sure you're not making mistakes. But do not take the time to re-check, nothing like that. Simply accept the chance that a mistake was made.
A reasonable manager will simply ask you to re-do it if necessary. That's fine. Graciously re-do it. A poor manager will yell at you or otherwise make a big production. At that point, you need to start thinking, it's easier to find a job with a job, being very strategic at work (it's still going to be a lousy situation even with the best strategy and brief diplomacy). Hopefully, you have a manager on the good side.