C.M.
Kids lie because they think it's a better choice than the truth. There is always something to be gained by lying.
My daughter is also 10 and I've found that immeditate punishments work better than ones that take place the next day. I would get a little more creative if I were you. For example, if he lied to get his sister in trouble, then his punishment would be to do something nice for his sister. Maybe he has to vacuum her room or do one of her chores.
Once he's done his punishment, ask him if the lie was worth it. Sometimes I have to ask my daughter that. It just reinforces what I'm trying to teach her.
If I were you I'd try to make him either do above and beyond what he lied about or the opposite. So if he lies about taking out the trash, then he should have to take out the trash plus another chore. If he lies about cleaning his room then he should have to clean his room plus another one. If he lies to get his sister in trouble, he should do something nice for her. Make it immediate. That always works best for us.
Good luck!