Is it a problem that my CV rounded-up my GPA while my transcript shows more digits?
As pointed out in the comments, you didn't lie.  Your actual GPA was a 3.8.  By contrast, it'd have been a lie if you claimed a 3.80.

I suspect that reviewers who see this may have one of three reactions:


No concern.  They'll see this as entirely correct rounding and not bother thinking about it any further.
Concern about fudging.  They'll wonder why you chose to report your GPA on your CV to just 1 decimal place, as this is a bit atypical, and coupled with the fact that it resulted in a round-up, it may come off as a bit of fudging.
Think it dishonest.  Committees in STEM fields should really understand that a 3.78 is a 3.8; that's basic numeric literacy.  However, if you're applying to a field that doesn't use math, they may perceive it as dishonest.


Personally, if I read a 3.8, I'd have taken it as implying anything from a 3.75 to a 3.84999..., such that the revelation of a 3.78 would be entirely expected.  I'd have found your decision to report only 1 decimal place to be dubious, but I'd have already judged you for that upon seeing your CV.  Seeing the transcript confirm that the GPA was on the lower end of the spectrum would strengthen the suspicion of intentionally trying to fudge the numbers, but since I'd already have been suspicious of that, it wouldn't really change much.