I just vaccinated my dog and now have to register her?

So I vaccinated my German Shepherd the other day and they gave me this letter to send to the city of Houston called City of Houston animal way home registration. this is new to me because before I had another dog this wasn't a thing. so what is? Is it necessary? Or is it just another way to get more money out of us? I'm honestly asking because it says that I have to send money to them. Do I have to do it? I live in rural house with a gate and metal fence she's not getting out she gots an acre to play with so I have no need for this if it's just for my pets to be able to come back home in case she gets lost. and what is the penalty if I don't pay it?