I believe the Sales Tax is ON TOP of the other Taxes.
If the Gasoline costs $2.00 a Gallon, the Sales Tax where I live would be about $.16 a Gallon.
Add the Federal and State Gas Taxes that inflate the cost to $2.70 a Gallon and the additional Sales Tax would be about $.20 a Gallon.
Every penny counts.
The State of CA is making more of a profit on Gasoline than the Companies who produce it.
Free money!