It must use some data in order to show the ads but in my experience it's just a bit of noise in a 3GB quota. I wouldn't worry about it.
A much better use of $5 is to get some World credits, not necessarily for making overseas calls but to avoid losing your account to inactivity. See Why Was My Account Deleted? [I'm not sure but I think accounts become inactive after 60 to 90 days of idleness. That may be an issue for casual users.]