If you do business with a company that just operates out of a state outside CA then they will not charge you sales tax.
However, companies like Home Depot have stores in all 50 states. Therefore, they will charge on sales tax for items you purchase over the Internet.
CA sucks tax wise and they are now trying to say if a company has an Internet Service Provider in CA they have a presence. Amazon.com just closed down all their business entities CA customers.