I was so nervous that it took me forever to count change
Why did you need to count change?
I was at work.
Well, at work you can't always walk away and then start again. Just take a deep breathe or two and focus on the counting.
Yes that is what I did, about twelve deep breaths later I was able to focus again and recount everything correctly.
Deep breaths really help me feel relaxed. I learned this technique while away at college.