The rate of the tax imposed by Section 3.24.010 shall be one-half (½) of one percent (1%) of the selling price or value of the article used, as the case may be; provided, however, that during such period as there is in effect a sales or use tax imposed by Grant County, in which the city is located, the rate of tax imposed by this chapter shall be four hundred twenty-five/one-thousandths (425/1000) of one percent (1%).