After the investigation of the employer, the director shall certify to the tax administrator the total amount of nonvested pension benefits that are includable in determining an employer’s tax liability under this chapter and the amount of those benefits that have been compromised or settled to the satisfaction of the commissioner. The tax administrator shall determine the amount of an employer’s tax liability under this chapter and shall notify the employer of the amount of the tax. The tax shall be due and payable to the tax administrator on the date that the employer ceases to operate its place of employment and shall be a lien upon all of the employer’s assets within this state. If the tax is not paid when due, the employer shall be liable for interest on the amount due at the rate of six per cent (6%) per annum until the tax and interest are paid.