The Taxpayer is a New Mexico business with a history of failing to file timely gross receipts tax returns. In October 1999, the Department audited the Taxpayer’s payment of gross receipts taxes for the period January 1996 through June 1999. When the Taxpayer received the audit workpapers in September 2000, he mistakenly believed that he was entitled to a cash refund when he actually had an outstanding tax liability. In May 2000, while the Department’s audit was still ongoing, the Taxpayer stopped filing his monthly gross receipts tax returns. In August 2001, the Taxpayer filed back tax returns for the period May 2000 through July 2001, but did not include payment with the returns. The Department then assessed the Taxpayer for the outstanding tax principal, plus penalty and interest. The Taxpayer protested the assessment of penalty and interest, and the Department agreed to abate penalty based on the Taxpayer’s misunderstanding of the audit findings and his right to a refund. At the hearing on his protest, the Taxpayer argued that the Department’s decision to abate penalty established his right to an abatement of interest. The Taxpayer also raised the issue of estoppel, maintaining that the Department misled him into believing he was entitled to a refund and did not have to report or pay current CRS taxes until the refund was received. Held: (1) The assessment of interest is not designed to punish taxpayers, but to compensate the state for the time value of unpaid tax revenue. Because the assessment of interest serves a different purpose than the assessment of penalty, the Department’s abatement of penalty does not provide a basis for abating interest. (2) The Taxpayer’s assertion that he failed to file CRS returns based on advice he received from the Department was not credible. The evidence shows that the Taxpayer failed to file because of cash flow problems resulting from a downturn in his business, and penalty was properly assessed. Protest denied.