That was exactly what I wanted back in The Sims 4 and that I would think it would come in Get to Work.
There was a mod for this function. He added back the objects of The Sims 2 to buy items from the game. But there was no interaction to pay in the cashier, unfortunately.
This mod is outdated and no longer works.
I hope you will come back officially with this feature in a free update for anyone who has EP Get to Work. Or a stuff pack, with functional shopping items: Bags, supermarket trolleys, cash register with employees getting the money, people in line...
http://www.sunni.us/greenway/Greenway-shop1.jpg http://www.sunni.us/greenway/Greenway-Cashier2.jpg
So many details around that would give so much realism to the game. :(