Can my manager make me replace change in the queue

So I started working at a sweet shop in July last year and I like the job. It's good but there's one thing that feels kind of weird to me. And I don't know if it's legal or not. So there have been occasions when we're closing the shop and once we count the money we are short a little bit if this happens. It's normally nothing more than like 20p nothing big but my manager says that when that happens. We have to make up the difference with our own money. Is that legal? It doesn't feel like it should be but I don't know. I work in London. Thanks in advance for the advice