The margins in a supermarket are around 1-3%. Let's say a cashier rings up goods worth $100 in 2 mins, if the queue is full they are ringing up $3000. Let's say there are 5 lanes, that's 15k in an hour. At 3%, that's $450 in profit. This store would need at least 10 employees total which brings us to $45/hr for each employee. And these are the best case assumptions – the margins are probably lower, the queues are never full all the time. So the actual value is probably like 20/hr or so.
So if the capitalists made 0 profit, that's what they could increase your pay by without losing money.
What do you think is the profit you produce for your company?