It's unlikely Amazon would be scamming using this method; the fines involved would be horrendous. It would only take one person noticing to trigger an investigation and audit by the state.
From most of the responders to this thread, this is unlikely to also be a mistake. But even if it were, Amazon wouldn't be keeping the money, but would be handing it over to the NJ tax authorities. (That would also probably result in a fine, but not a catastrophic one.)