Each person doing business as a plumber, steam fitter or operator of a tin shop or roofing shop shall pay the following license tax: In towns or cities of 50,000 inhabitants or over, $25; in cities and towns of 10,000 inhabitants and less than 50,000 inhabitants, $15; in cities and towns of less than 10,000 inhabitants, $10; and in all other places, whether incorporated or not, $5.