Revenue bonds shall be sold at not less than ninety-five percent of par plus any accrued interest. Such bonds may be sold at private sale, or such bonds may be sold at public sale after notice of such sale has been published once at least five days prior to such sale in a newspaper circulating in the municipality. State or national banks may purchase bonds from each issue of revenue bonds issued under the provisions of this chapter in an amount not to exceed at any time twenty-five percent of the unimpaired capital and surplus of the bank.