C.R.S. § 39-26-109

If the accounting methods regularly employed by the vendor in the transaction of his business, or other conditions, are such that reports of sales made on a calendar-month basis will impose unnecessary hardship, the executive director of the department of revenue, upon written request of the vendor, may accept reports at such intervals as will in his opinion better suit the convenience of the taxpayer and will not jeopardize the collection of the tax. The executive director may by rule permit taxpayers whose monthly tax collected is less than three hundred dollars to make returns and pay taxes at intervals not greater than every three months.