I apologize. I did a deeper dive...
One of the exemptions was intra-state commerce. If your grocer was local only, it was exempt from fed minimum wage.
The law starting changing beginning in 1961 and again and again over time from there.
Grocery chains were not very common in these parts at the time. This was a small town 'rural' grocery store.
Still, if the pre-war wage was 25ยข, by 1957 it might have been around half a dollar. Simply, I have no memory of any minimum wage discussion at that distant date.
The Supreme Court has developed such an expansive definition of interstate commerce that a farmer selling watermelons on the side of the road is covered because someone from another state could drive by and buy a watermelon. Hopefully the current Court will get a chance to rein in this excessive interpretation.