Not if it’s just in your Roth. As you say the basis is used to work out how much is to be taxed on sale, and in a Roth that answer is zero.
Awesome. This has been at the back of my mind forever. The broker that I was working with actually used the cost basis thing as an argument for me NOT to move to Fidelity, but I ignored him because it felt like he was playing me to some extent. (I think he eventually did mention about a roth, but it was a while ago and I can’t be sure). It’s been at the back of my mind to figure this out for a long time now, but I’ve just been too lazy to google. Well, that’s another relief. Thanks so much @Alistair!
Yeah, what he said! :D