What taxes do you mean? Are you talking about sales taxes when you purchased them, or are you referring to personal property taxes charged by some states? (i.e., I live in Virginia, which charges me an annual property tax on the value of my cars)
If you're talking about the sales taxes, you might be able to. State and local sales taxes have been deductible for several years. Note that if you elect to deduct those, you can't also deduct state income taxes on the same return. You could amend your tax return to claim this deduction. However, returns are amendable only for the past three years, so you might be outside the window if you've owned the cars for three years.
If you mean property taxes, yes, they are deductible, so long as you itemize. You would include them with any state income taxes you deduct. Be careful not to deduct money paid for things like proof-of-payment decals, however.
Hope this helps.