The issue is that I'm stupid, i figured it out lol. Thanks
First you click and drag the items onto the scanner, this will tell you the total price. Then you click the register and it will open. On the right side you will see a tray with the money the customer gave you. You have to drag it into the register and drag the change on the tray. You can also click on the post it note on the register in the top view to see the value of the coins. Once you collected the money and put the change on the tray (this is where i got stuck) you have to click the base of the open register in the bottom screen (basically just below the coins) to close it and complete the transaction. I was trying to somehow drag the change onto the customer but that doesn't work