No. It's governed where the sale took place. The visitor to California who buys something taxable while in California pays California sales tax. If he purchased it online from Nevada, he's not subject to California sales tax -- thanks to the commerce clause in the US Contitution.
Thank you for the clarification. This came up a few years back when Californians were going to Oregon (which has no sales tax) to buy vehicles that were then brought into California.
California tried to collect a tax on the vehicles but the courts did not allow it. How is buying a car out of state different from buying a post card?