If any real property is subject to sale at the same time for delinquent general taxes and also for delinquent special assessments or installments thereof, the delinquent general taxes and the delinquent special assessments or installments thereof shall be advertised and sold together in one sum and one certificate shall be issued therefor. If the real estate is sold for both delinquent general taxes and delinquent special assessments or installment of special assessments and there shall be no bidder therefor, the county auditor shall strike off the parcel of land to the county and one certificate of sale shall cover both general taxes and special assessments which are delinquent.