The US has a single centralised government with a single currency, Europe is not.
You've partially right....we have a single currency, but we do NOT have just a single centralized government.
The Federal govt. is and is supposed to be somewhat weak...and its few enumerated powers are in the US constitution....
The real power that actually governs the people for the most part, resides in the individual states. That's how we have VERY varying laws in many respects.....there are some cases the SCOTUS has had to take over the years, mostly on equal rights, etc....to establish that are constitutionally the same across states, but for the most part, everything that affects a citizens' life daily is governed by the laws of the state they reside in....so, financial laws, tax laws (state and local)...etc can all vary by state.
Most states have sales taxes..some do not. Some do not have income tax and others do...some states require car inspections annually, some to not and even those that do, vary in what they check..most do not check emissions if I recall correctly....
So, the US has. Federal govt that manages the currency....and is a singular face to the world....but internallly it's largely a mishmash of state laws that change as you cross state borders...