Self-checkouts, like many problems, seemed to be solved when I visited Japan. They have 3 stations, 1 where an employee scans your items and then puts them back into a new basket. They then direct you towards (one of many) terminals where you pay. There are then more spaces where you can bag your groceries.
Once you've seen it you'll be baffled as to why it isn't a global solution. No need for the employee or others to wait while you count your coins or bag up, and no need for anyone to wait behind you while you wait for the self-service checkout to weigh each item individually, fail to scan etc.
https://www.standard.co.uk/news/uk/commuters-ordered-to-repa...