Washington state, for example, has a digital goods sales tax that applies to everything from streaming music and movies to e-books. Florida, meanwhile, taxes streaming video but not digital books.
Many sellers already collect these taxes. For example, if you live in Washington, where Amazon.com is based, you're already paying tax on digital purchases. Apple already collects sales tax for iTunes purchases in states where digital music is taxed, according to its website. And Netflix also already collects tax where applicable.
To find out what items are taxed in your state and at what rate, contact your state's tax and revenue agency. A map with links to the 50 state tax websites can be found here.