I agree with brawlex and bulblax, it's not good, but people are blowing it way out of proportion. My ex girlfriend used to steal money from her parents occasionally, but she isn't a kleptomaniac now, she's never stolen from a store and she never plans to. It's easy/convenient/sometimes justifiable to take a small amount of money from your parents sometimes, especially when you think you can get away with it. Comparing it to stealing a car IMO is a terrible comparison. Killing a bug isn't the same as killing a person, do you know why? Because a bug is not a person, the act is the same but the consequences are vastly different and one is obviously much worse than the other. Stealing 20 dollars is kind of stupid, but stealing a car is a whole different stories.
And yes, most stores do care what you steal, it's common for stores to not prosecute people caught stealing items of less than 20 dollars in value. It's illegal in some states to prosecute people caught stealing medication or bread. So again, the act doesn't determine the consequences.
My suggestion, you'll get away with it probably, but stop doing it. It's wrong, your parents do a lot for you, seriously, just ask them. If that doesn't work get a job and buy your own points. Someday you should probably come clean about it to them too, and pay them back.