In microeconomics, we often discuss what are called "compensating wage differentials". Because of demand and supply forces, additional money is needed to convince workers to accept higher risks to their life. This is part of the reason that workers who stand on the side holding a sign earn much more than your average fast food cashier, despite that fact that being a cashier at a fast food restaurant takes a higher skill level. (The same logic can give us insight into why your average plumber often makes a higher income than your average elementary school teacher.)
I have heard that night-shift workers at gas stations were in more danger than police officers. This graphic shows only "cashiers", but I'd be curious to see the risk for that specific sub-group (overnight cashiers at gas stations).