C.R.S. § 39-26-116

It is the duty of every person engaging or continuing in business in this state, for the transaction of which a license is required under this part 1 to keep and preserve suitable records of all sales made by him and such other books or accounts as may be necessary to determine the amount of tax for the collection of which he is liable under this part 1. It is the duty of every such person to keep and preserve for a period of three years all invoices of goods and merchandise purchased for resale and all such books, invoices, and other records shall be open for examination at any time by the executive director of the department of revenue or his duly authorized agent.