Surely the point of all this is to reduce the costs the store has to meet.They should then pass some of those savings on make their products more attractive to customers.
How do you know they don't? The prices charged to customers are going to be based in part on all the wide variety of costs that supermarkets incur, including staffing, technology, the cost of buying the food, rent, etc. Unless you have detailed access to the supermarket's private accounting information, there's no way for you to tell exactly how each supermarket decides what price to charge each food item.
However, supermarkets are not, on the whole, monopolies. They operate in a very competitive environment in which any customer perception of price differentials is likely to see custom migrate to their competitors. In that environment, it would be astonishing if any savings the supermarkets make through technology don't have some effect on the prices they charge.
You stated it was new technology. I am stating it is the same technology as it has always been although I will happily admit it is held in a nice new box.
The technology for self-service checkouts appears to include:
1. The ability to automatically work out what money you've paid, and give you back the correct change.
2. The ability to weigh the items you've bought and cross-check against the expected weight of what you've bought (albeit, as a few people have commented, not 100% reliably) in order to prevent fraud.
3. A customer-friendly UI.
None of that is revolutionary, but it's all important for self-service checkouts, and presumably not particularly required for manned checkouts. And I would imagine that none of that would have been possible to implement in a cost-effective and reliable manner, say, 25 years ago. So it does appear to answer to the description 'new technology'.