According to an article, "Colorado Department of Revenue officials confirmed Amazon's plan to charge and remit collections from Colorado's 2.9 percent sales tax."
"State law requires online retailers to track purchases made by people in Colorado and to report the amount of sales tax that should have been paid. The companies also must advise the buyers of their tax obligations. Under federal law, retailers that don't have a presence in the state can't be forced to collect the taxes, triggering the self-reporting requirement by consumers."
A handful of states have already joined Colorado by taxing Amazon sales. For example, Michigan began collecting sales tax in October 2015.
Legislation is being proposed and considered that will change tax laws across the country and online. Vertex Inc. has designed an innovative interface and user experience that reduces the time, effort, and risk of managing sales tax compliance.