>>145I always equated "que le vaya bien" with "have a nice day" when it comes to clerk/customer exchanges. It's not what it literally means (in English it would be "Que tenga un buen día") but I think it's in the same spirit. "Fare well" is a better fit ("May you fare well" is the prefect translation), "Good luck" kind of fits too.
"Que le vaya bien," expresses one's wishes for the person to do well in their endeavors or for good stuff to happen to them.