Online retailers that sell to California customers must collect sales taxes beginning April 1 – and not only for the state. They also must collect and remit sales taxes for individual districts in which their total annual sales exceed $100,000 or separate transactions number 200 or more.
California will begin requiring these sales-tax collections in response to the U.S. Supreme Court’s 2018 South Dakota v. Wayfair decision. The ruling affirmed a state’s authority to put the same sales-tax obligation on online retailers as on brick-and-mortar retailers.
In California, district taxes are voter-approved sales and use taxes imposed by cities, counties and other local jurisdictions. Retailers can find the tax rates for each district here: http://www.cdtfa.ca.gov/taxes-and-fees/sales-use-tax-rates.htm