How to pull off the short change con bar trick

This episode, we're turning to the dark side and learning actual CRIME. Remember, the following is for informational and educational purposes only!
Everyone's heard the term "short change," but very few people know about the actual street con for which it's named. This scam is performed thousands of times each year, and con men score millions of dollars just by using a few simple verbal tricks...

THE GOAL: To get more money out of the register than you're entitled to, without the attendant even realizing it.

THE METHOD: In this episode, we're presenting one of the simplest versions of the short change. Advanced versions of this scam can take people for hundreds of dollars. This version uses three phases:
Start by peforming some kind of fair trade to get the register open. You can ask for change for a twenty (looking for a ten, a five, and five ones), or maybe buy an item and pay with a large bill (for example, buy a beer with a twenty, giving you the drink, and $15 change). It doesn't matter. All that matters is that you start with a fair trade that involves a lot of bills. This gets the register open and the attendant's head filled with a bunch of numbers, which sets you up for...
PHASE TWO: THE SECOND LAYER (INCLUDING DISTRACTION). This is a trade you'll start on top of the first one. It's a trade that's ALMOST fair, but involves a mistake that makes the short change possible. In our example, while the till is still open, explain that you've got some ones to get rid of, and that you'd like to trade them for a $10 bill. Drop down a stack of $1 bills (actually containing only 9 of them), and scoop up their $10 bill (along with the change from PHASE ONE). Remind the cashier to count those bills and "make sure it's right" (again, this fills the cashier's head with more numbers and builds some time delay).