This deals with both criminal law and civil law.
On the criminal law side, this is: embezzlement (taking sales from an employer and directing those funds to the employee); and fraud (misrepresenting the services sold to the third parties (dog walking,etc.) - although this second one is probably not really an issue).
On the civil side, this is: "conversion" (the civil equivalent of theft) from the employer, and "fraud" (for anyone that was billed on the credit card reader), both of these are "intentional torts" so the holder is responsible not only for the actual damages, but can also be liable for "punitive damages" (meaning the court can award additional money damages to the plaintiff to punish the defendant's wrongdoing).
A person that has engaged in this kind of conduct really should speak with a local criminal law attorney to discuss this situation. Having an embezzlement conviction (or even arrest) can be very harmful for your future employment prospects. You will want to talk to an attorney very early on, as they can help you strategize a resolution, and if appropriate, negotiate for a resolution without having to admit guilt (see, if the individual were to approach an employer with this information, they would be admitting to the wrongdoing, creating an admission of guilt, while an attorney can do the same thing on behalf of their client, but be able to do so without the client actually making an admission of guilt).