When real estate described in a mortgage is exempt from taxation under the Constitution of the state of Minnesota, article X, section 1, the mortgage registry tax shall be paid to the treasurer of the county in which the real estate is located in the same manner as if the real estate were not exempt from taxation. When any real estate described in a mortgage is not exempt from taxation under that section, but is not taxed by direct tax upon the net tax capacity thereof, the mortgage registry tax shall be paid to the county; this sentence does not apply to real estate taxed under sections 298.23 to 298.28.