Every person engaged in the business of selling radios or other receiving or transmitting machines shall pay the following annual privilege tax: In cities of over 50,000 inhabitants, $25; in cities of over 15,000 inhabitants and not exceeding 50,000 inhabitants, $15; in cities and towns of over 5,000 inhabitants and not exceeding 15,000 inhabitants, $10; in cities or towns of over 1,000 inhabitants and not exceeding 5,000 inhabitants, $5; and in all other places, whether incorporated or not, $3.