Used Car Sales Tax, which value is the 6.25 being calculated?

I know that in Texas 6.25 is the charge that the DMV charges on used car sales tax, but which value is it on? Trade-in, Private party, or suggested retail? Also which is the condition they consider excellent, good, or fair?Used Car Sales Tax, which value is the 6.25 being calculated?
on the "net" difference before fees tag etc.Used Car Sales Tax, which value is the 6.25 being calculated?
The tax is calculated on what you actually paid for the vehicle. Or price given to you for your trade plus what you paid for the vehicle if a trade applies.Used Car Sales Tax, which value is the 6.25 being calculated?
the 6.25 % tax is on everything, uncle sam gotta get paid.

Q2) Condition of a vehicle @ trade in is a totally RELATIVE and SUBJECTIVE judgement. do you remember the song " I say potato, you say po-tah-t-ohh". So if you think that a buyer (or dealer) is under rating your cars (trade-in) value, you can always seek another opinion. But remember you might get the same answer again.