S.D. Codified Laws § 42-7B-31
Any person required to file returns or reports under this chapter, who fails to file a return or report which includes all taxable transactions within fifteen days following the date the return or report is due is subject to an additional amount, assessed as a penalty, equal to fifteen percent of the tax or ten dollars whichever is greater. However, for reasonable cause shown, the executive secretary may reduce or eliminate such penalty. Any person subject to tax under this chapter who fails to pay the tax within the time prescribed is subject to an interest charge of two percent per month or part thereof for which the payment is late or five dollars whichever is greater. Penalty and interest are considered the same as tax for the purposes of collection and enforcement including liens, distress warrants and criminal violations. Any payment received for taxes, penalty, or interest is applied first to tax, beginning with the oldest delinquency, then to interest and then to penalty. The executive secretary may, upon application of the taxpayer, establish a maximum interest rate of thirty-six percent upon delinquent taxes if the executive secretary determines that the delinquent payment was caused by a mistake of law and was not caused by an intent to evade the tax.
SDCL 42-7B-31