"How could this have been designed better?"
By having one confirmation step, not three.
The action should have been: perform action > confirm action
Standard practice is to prevent error states and that's why you have the confirmation step; that's the error prevention.
In some systems where the action can be profoundly negative you may have a confirmation of the confirmation: perform action > confirm action > finalise action.
In no system I have come across would one have a triple confirmation. That's just bad design or an action like confirm nuclear launch codes.
In your example, one has to weigh up the consequences of the action versus the frequency. I doubt this cashier performs infrequent very negative actions. S/he will perform frequent, mildly negative actions.
Triple conformation is just bad design. Use single.