I'll bet if they don't have locked dumpsters and you dove the dumpster for a week and inventoried you would be amazed at how much is tossed... Of course it will vary by store, a small store with a limited produce selection will obviously toss less then a store with a huge produce selection...
It's estimated that something like 60% of all food produced/grown in the US ends up in landfills, it's mind boggling to consider just how much volume of waste that is...
I haven't seen any dumpsters and actually, I just remembered my driving school is in that plaza and the road test practice is behind it, which also happens to be the load in for the store, and I haven't seen any dumpsters but they must have one somewhere. I actually think msybe last year or a couple years ago they started selling the older stuff. They sell half priced meat on certain days too. They used to toss everything and I thnk trader joes started not so our local grocery did too or they made a law or something i think