At least at Sam's or Costco, those are not stores open to the public. All rights are waived with membership fee.
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.