SDCL § 43-26-9: Prepayment privilege implied in real estate contract.

Any contract made in this state for the purchase and sale of realty shall be interpreted as including an agreement that the vendee shall have the right to tender, and the vendor shall have the duty to accept, prepayment of the balance of the contract price with accrued interest at any time without penalty to the vendee, unless the contract expressly provides otherwise.