Upon every person engaging or continuing within this City in the business of selling any tangible property whatsoever, real or personal, including the sale of food, and the services incident to the sale of food in hotels, restaurants, cafeterias, confectioneries, and other public eating houses, except sales by any person engaging or continuing in the business of horticulture, agriculture or grazing, or selling stocks, bonds or other evidences of indebtedness, there is likewise hereby levied, and shall be collected a tax equivalent to fifty one-hundredths of one percent (0.50%) of the gross income of the business, except that in the case of selling at wholesale, the tax shall be equal to fifteen one-hundredths of one percent (0.15%) of the gross income of the business.