To stick it on

[Chicken Sandwich]

This is a dialogue from the tv series Extras:

00:11:12,040 --> 00:11:13,598
-So you don't do celebrity discount?
-No.

207
00:11:13,680 --> 00:11:17,992
-No, not 1%? Couldn't give me 1%?
-Oh, okay. I'll do you a 1% discount.

208
00:11:19,120 --> 00:11:23,159
-What's that?
-On £2,500? £25.

209
00:11:23,240 --> 00:11:26,596
Not worth it.
I'd rather you stuck it on if anything.

Can someone explain what "to stick on" means here? Is this the phrasal verb "to stick something on"? The COED defines this as: Place the blame for a mistake or wrongdoing on. However, I still don't get it.

[JMurray]

The character in this episode of Extras is pretending that he has plenty of money and can pay for his friend's dress. However, he still tries to get a discount but it turns out to be such a small amount that he says to the saleswoman, don't bother taking the £25 off the price, in fact you might as well stick it on… that is, add it to the price. So he is trying to get a discount while at the same time pretending that he doesn't care about the money.

not a teacher