Sales tax paid is typically just a cost of the item being purchased unless that item is held as inventory.
If you are reselling fuel, then you can get a sales tax credit against that purchase (though typically you fill out hand to the vendor a reseller permit so he can sell to you sales tax free). Book the sales tax amount as a sales tax paid expense, and later when you pay sales tax, you adjust the amount due by the expense amount for that reporting period - zeroing out the expense.
But, CA does have some weird rules, I would suggest you get with a state tax accountant and insure that you can take a sales credit for the purchase of fuel. Last thing you want, is to do it wrong and incur a sales tax audit.
