Yeah they are. Typos and errors show that you don’t look over your work and don’t put effort in to fix it.
You wouldn’t submit a resume if it had common spelling errors would you?
It might not be the straw that breaks the camels back, but it could mean the difference between this candidate and another.
I mean, if someone sends a resume or cover letter that's completely riddled with typos or grammatical mistakes it's definitely not going to do well, especially if there's competition that doesn't have the same problems.
But if there's 1 or 2 typos it's definitely not a deal breaker.