Places such as these usually have supervisors most of whom do not have a clue about managing anything and probably would not get a job managing elsewhere. The attrition rate of staff in most fast food outlets is high too but in our current financial state some hold on to any kind of job for longer.
But, forcing staff to cough up for "shortages" is the pits. The managers are abusing their status but probably have not the cop-on to be any other way. I would bet that any employee in such a situation as described here would be wasting his/her time trying to reason with the supervisor.