Don't tell a lie

Is it still wrong to lie if it's to keep your child from lying?
The new lie at our house is Santa knows every time you lie and he takes away one of your presents.
Here's a brief rundown of how the conversation goes:
Me: Bryce, did you wash your hands after you went potty (yes...I actually do use the word potty)?
Bryce: Yes
Me: are you sure... I didn't here the water?
Bryce: Yes Mommy, I washed my hands
Me: Bryce, are you lying to me?
Bryce: No way mommy
Me: okay...but Santa knows if your lying and he will take away one of the toys he was going to bring you
Bryce: Mommy, I said I washed my hands
Me: Alright. I hope you are right. I think he had a tractor for you. If you tell me a lie he will have to give it to another little boy
Bryce (after several seconds of deep thought): FINE...I didn't wash my hands. I'll go do it right now. will Santa still give me my tractor. can I tell him I'm sorry?
Me: If you tell me your sorry and promise to try to only tell the truth I think he will forgive you

I guess I will have one less present under the tree this year too!!