The auditing process for cash transactions is centered on the fact that every employee who receives cash, whether from guests or the company's cashier, must have a Cash Account registered in his name.
This will cause the employee to have the [Cash] option during the posting of the receipt on the Reservation:
With this, the posting will be automatically validated and your employee's Cash account will have the updated balance.
To reset your employee's cash balance to zero, check his or her balance on the Financial Dashboard and then make an Internal Transfer where the amount leaves the employee's cash and goes to one of your Bank Accounts or Central Cash.
Now that you already know how to audit cash transactions, how about reading more information on the theme?