A Simple Answer to Withholding Amount

I hope for some clarity here, please. For the past three years, I have owed $1k+ during the filing season. My tax situation is fairly simple. For income, it is just one job (one W-4) and some interest from a savings account. I claim "0" on my federal and state forms.

 

Why do I still owe so much come tax season? Are commissions taxed at a different rate?