Haha, as a Brit, I have quite a few eurocent coins in my foreign loose change drawer.
Also, as a Brit, if I bought something for £9.99 and gave them a £10, I'd expect change. If they said they didn't have any 1p or 2p coins, I'd expect to receive a 5p coin instead. And when I say expect, I've been offered that a couple of times in the past in that situation, I've never had to ask for it.
They don't call this "the rip-off republic" without reason
So why? Maybe the vendors reckon it will work out in their favor this way.