Most cams should work fine but some might need some lens twisting to be in focus maybe 4 feet down. Domes are better to keep from being bumped on a low ceiling than bullets and can keep people guessing more than turrets exactly where the lens is pointing. 4mm vs 2.8mm would depend on how much detail you want on hands and the money vs a wider FOV but I bet you'd like a 4mm unless you had no other cams there and wanted to see more around the till. You could dial in exactly what you prefer with a varifocal but they're more money. Which exact cam or brand might depend on what NVR you plan on using with it. Hikvision NVR? Probably if you're asking in a Hikvision forum so a Hik cam. This one isn't the cheapest but is reasonably full featured and should handle challenging lighting a bit better than older ones if the register is near a window- DS-2CD2122FWD-IS. It has an alarm input if you want to hook up a contact switch on the cash drawer.
