Burrito cart tipping dilemma

[SomethingClever]

There's a delicious burrito cart near my office that I hit up frequently for lunch.

Most items cost $4. They have a tip jar sitting out, and I frequently see people buying $4 items with a $5 dollar bill, then tipping the $1.

I have a couple problems with this.

1) Since this is a burrito cart, the people you're tipping are the owners. So what's the point? I'd happily pay $5 for a burrito if they decided to charge that much. All the money is going to the same people anyway, so what does tipping accomplish?

2) Since all their items cost a round dollar amount, one would have to usually tip a full dollar unless one carried change on his person. I do not make a practice of this. $1 tip on a $4 item seems excessive.

3) It's a freaking burrito cart! It's not like I can sit in some nice atmosphere while they prepare my food. I have to stand outside and wait.

4) The service is very very very slow. Friendly, but slow.

Am I wrong to not tip $1 on my $4 burritos? Their food is great; I guess I see it as lame that they have this tip jar out rather than just charging what they want to get for their burritos.