Each person operating a shop for the repair or rebuilding of machinery or making parts therefor for the public and charging for same shall pay the following license tax: In cities or towns of 100,000 or more inhabitants, $40; in cities or towns of 50,000 and less than 100,000 inhabitants, $25; in cities or towns of 15,000 and less than 50,000 inhabitants, $15; and in all other places, whether incorporated or not, $5. This license shall not apply to what is commonly known as a blacksmith shop or to shops repairing automobiles where a garage license or an automobile repair license has been taken out.