Where does it show that I had $40 extra per month taken out for taxes?

[k8deekay]

I elected $20 per paycheck and I get paid every two weeks.

[BobB7 · Accepted solution]

Box 2  of your W2 shows your withholding tax, including the extra, that was withheld.  You get credit for that when the taxes due or refund amount is figured.  If you entered the W2 as it reads, you don't have to do anything more.