OK, now don't freak out. Here's the full story.
A correct guess, right down to the penny, is very unlikely in general. But the reason she was asking me to guess is because the bill happened to be an integer dollar amount. Most people, when asked to guess a price, only give the dollars. That's what I did, and that narrows the number of options down by a factor of 100.
I didn't think it would be less than, say, $60. And I figured (hoped) it would be less than $100. So, given than I'm choosing an integer between 60 an 100, that leaves only 40 options. I guessed $98. NAILED IT!