A Sup­ple­men­tary Ser­vice Occu­pa­tion Tax is here­by imposed upon all per­sons engaged in the busi­ness of mak­ing sales of ser­vice with­in the Coun­ty of Union, Illi­nois, at the rate of 1/4 of 1 per­cent of the cost price of all tan­gi­ble per­son­al prop­er­ty trans­ferred by such ser­vice­men either in the form of tan­gi­ble per­son­al prop­er­ty or in the form of real estate as an inci­dent to a sale of service.