If they're really stealing tips and they're a decent sized org (if they have dedicated HR) that's a major suit. Another one is not paying OT. We see class actions for this all the time and it wouldn't be hard to get a plaintiffs firm to take this case on a 30% contingency.
HR is likely just trying to go through their motions, tell you all the things they're required to (or want to). It's more likely that they want to explain some reason/cause for your termination, whether real or made up, just so it's on record. If you skip the meeting id guess they will email/mail you a bunch of shit to cover their ass.
I doubt its that they discovered some wrongdoing by management. In that case the usual strategy is to make the terminated employee jump through the hoops of recovering (demand letter, suit, etc). It's usually a small amount (for the single employee) and employees are disorganized and can be pushed around.