Marketing engineer for marketing people, design engineer for designers, sanitation engineer for janitors — so by that logic, cashier engineer would be next for the people who ring you up at checkout.
What is up with this title inflation? Why call yourself an engineer just because you write software? To me, engineers are people who build things and take full responsibility for them — designing a bridge where thousands of lives are in your hands, building an airplane engine, filtering a city's water supply. Not pressing keys on a machine.