The state tax on your car is not an income tax. You can not apply it to your tax due. It is a Sales Tax. Different kind of tax. The $600 tax on your W2 was probably in box 2? That is federal income tax withholding. It is just an estimate of the tax you will owe on your total income when you fill out your tax return at the end of the year. That's why you file a tax return to see if you had too much withholding taken out of your paychecks and get a refund or owe more tax.
Any state withholding will be on W2 box 17.
