Actually, there has been much research into whether or not coffee grounds make the soil more acidic and it turns out, they don't. I can't comment on tea bags but, the hypothesis behind coffee grounds having low acidity is that the acid is leached from them during the brewing process and I'm guessing that the same would happen with tea.
Cofee grounds do have a high N/P/K value and they apparently repel mites and slugs as well. So, they certainly won't hurt. I added them to my soil last fall and now, it is the nicest soil that you ever saw.