When I worked retail, you punched out and then left, even if you were the last ones around. Our Manager and Supervisors insisted you didn't punch out until you were literally leaving the building. Once we finished, we never waited for the manager to finish up and leave, we'd just leave for the fire door. Occasionally if we did hang around and wait for him we didn't punch out until he came out of his office turning the lights off.
Well, I know in my store the timeclock was on the opposite end of the building from where we would leave. And I think there was a policy where at least one person had to stay with the manager at all times (and open with the manager in the morning).
I don't know. It never seemed to bother any of us.