Oddly enough I've worked as both a cashier sometimes watching over self-checkouts and also as an engineer in a company that manufactures self-checkouts (although I worked in a different department and only occasionally helped out with the checkouts). They can log that stuff no trouble. They cancel it as far as the customer sees, but that doesn't mean anything for what it keeps behind the scenes. At least on the ones I worked with, there was the option for cashiers to retrieve the most recent state and print it out as a receipt either for the customer or to scan it to transfer to another checkout