Why do some websites charge a sales tax on purchases while others don’t? Most retailers do not have to charge taxes for online purchases made in states that they do not have a physical presence. State governments are missing out on billions in tax revenue, but smaller e-retailers contend the patchwork of nearly 10,000 different sales tax rates and policies make coordinating payments prohibitively difficult. We talk with experts about why you are (or are not) paying taxes on the Internet and the changes that may be in store for e-commerce.