However, home depot is open to the public.
The laws are fuzzy. In one sense, it's YOUR property once purchased, not THEIRS.
However, there has to be a probable cause to be detained, even in a private shopkeeper setting, for it to be illegal to walk away when asked to view a receipt. The store (private property) could say 'fine, but you're banned from shopping here.'
I think you're right though, it's more about what's entered to the receipt than what's concealed elsewhere.