Let's say that each of these robots costs $10k per year, including R&D and maintenance. Let's also say that because of inefficiencies with having people order their own food or with assembly ultimately being done by hand, a store has to install 6 robots to replace 3 workers.
3 workers * $7.25/hr * 8hrs/day * 365days/year = $63,510
6 robots * $10k/robot = $60,000
So it is actually less expensive already to replace minimum-wage workers with robots. The minimum-wage issue has very little to do with it besides trying to keep wages low in general.