It's more complicated than that, really. Pizza delivery boy (of a really, really small company) might be one of the few examples where I wouldn't ask my money back. Even then, in 99,9 % of the cases the pizza boy wouldn't keep that money to himself, but pass it forward to the cashier instead and it would go directly to the company. That's because, again, we really don't have a tipping culture because everybody gets paid enough.
If it's a private entrepreneur or a small family company, it's much more common not to take the change because then you know who's gonna benefit from that. And trust me, it's really tough for small businesses in Finland because of taxes and regulations, so people want to support entrepreneurs.