Not in game, but where I live people do this at Fast Food Restaurants a lot.

I rolled through Mcdonalds one day for a 20$ meal for my kids, happy meals etc. And when I got to the window the teller told me the person in front of me paid for my meal and that I could either enjoy my free meal or pay for the person behind me. The guy behind me only had a 7$ order so I paid for his and got my meal 13$ off....

I went back the next day and she said the chain went on for 50+ cars and the guy that broke got a 30$ meal for free and wouldn't pay for a $1 sweet tea behind him....

In game, I pay it forward with dungeon runs, all though the requests have been down lately.