You'll find mixed reviews on coffee grounds for chicken bedding. Some people use it knowing the methylxanthines in coffee are toxic to chickens and a lot of other pets, as well. They say they have never seen their chicken try to eat it. That's like saying your pit bull has never bitten anyone. Until the pit bull bites someone.
Very recently, in the Emergencies forum, we had a frantic person with a small chick who had eaten the coffee grounds bedding. We tried everything we could think of to help them save this chick, but the chick died.
It's not possible to know if the chick died of toxic poisoning or simply constipation from the grounds clogging its intestines. But this is a real life anecdote documenting a very sad experience with using coffee grounds as chick brooder bedding.
Since we know the caffeine in coffee grounds is toxic and we know that baby chicks will try to eat anything, it's best to avoid coffee grounds for baby chick bedding.
As far as using it in the coop for adult chickens, personally, I would stay away from it. The risk isn't worth it.
As for the store using it in the chick tanks, store employees can be among the most ignorant of people when it comes to chick care and chicken knowledge. I certainly would not model my chicken care after a feed store's chicken care policies.