The question you really are asking, I think, is whether your old sales tax bills are still collectible if you are trying to register another car post-petition? This is a matter of state law. I would ask the question at the County Tax office where you reside. See what they say ... you may want to check with the County Counselor as well depending on the answer.
Whether or not sales tax is dischargeable in bankruptcy is a question of state law. It depends on whether or not your state defines sales tax as an "excise" or "trust fund" tax. If your state does define sales tax as an "excise" or "trust fund" tax, then the sales tax will not be excepted from bankruptcy discharge. In NYS, for example, sales tax is considered a "trust fund" tax and is excepted from bankruptcy discharge.
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