Well I have some POS (touch screens at the restaurants for your tickets/checks) experience so I'll weigh in on this.
First, this receipt looks like one that would come from a Micros ro Aloha POS system (I think) but keep in mind, a lot of POS systems can somewhat customize the receipts and tickets so Aloha, Digital Dining, Micros, Maitre D, and a ton of others could look like each other if they really wanted to. Most of the time though, they just go with the standard settup that the POS company had 20 years ago.
Anyway, I have most of my experience with Digital Dining and I know that we could manipulate a lot of wording and things in the receipt to do some really cool stuff like if you had a charge account with us how much you owed, when you last paid, etc. A ton of other stuff too and you could also put this in the receipt too. Even though Digital Dining had a standard calculation that would be correct, I believe you could actually go in and manually change the percentage because it wasn't "hard coded" into the software. If memory serves me correctly. I may be wrong but I think you could. So in this case, yes, you could change the calculation even though it "says" 15% it could be double or triple that if the person made the total on line x = 0.25 or whatever.
Like some have said, even though this option is in the software, it's really a terribly bad idea to put it on the receipt. It's asking for a tip but even more disgusting is it's telling you how much. Why isn't there a percentage for 5% or 10%? We all know why.
Not to hijack the thread and start a different subject but I do have an issue with people that tip based solely on a percentage. I was out on a date with my girlfriend once (and she worked as a server at the time) and when we got done, she got her calculator out and was going to start calculating her tip. Before she could start pressing buttons, I told her that I couldn't believe that she had the nerve to do that especially considering that she herself was a server.
If people are tipping based on a percentage, then they really don't have any idea why they're tipping other than other people do it and they feel that the "norm" is a certain percentage so that's what they'll do. If you want to show appreciation for your service, do it appropriately by tipping what you think would be reasonably sufficient. And for frick sakes, round up already. If you're ticket is 11.18 and you thought the service was good, just write $14.00 in the total line and call it good. If it was great, $15.00 or $16 would be nice. If it wasn't great but not terrible, just do $13. Not this, well $13 isn't enough but $14 is too much crap so I'll make it $13.50 because it's right in the middle. That's only $2.32 dodo head. Don't go out and eat if you can't afford to.
For the record, even though I was in the industry, I never thought tipping should be a way of life either like someone else on here said. An old bartender pal of mine once said the same thing but mentioned he didn't know when or where tipping originated or how it got to be so commonplace but he was going to take advantage of it. Hey, I will too but I wish that people in the industry could just get paid better and there wouldn't be a darn debate about tipping but that's another thread.