yes but will it be used??
Could I or anyone start their own currency?
Yes ... "currency" is ANY accepted medium of exchange.
So technically, even bartered goods are currency ... And people barter all the time.
What about Bitcoin?
Ever hear of the Bitcoin, sure you can create your own currency? I own my own business, I could offer my own currency like buy three of the services offered and you will be paid "THREE KOP DOLLARS". For every fifteen KOP DOLLARS you can buy a service. A limited currency, if I can find more businesses that would award KOP DOLLARS and honor them in their stores the currency works like the regular dollar. Could you pay your taxes with KOP DOLLARS, no but used at a store or service that accepts them your good to go.
USA currency No.
Sure .. But it is worthless if you don't have an entire system in place to create its value for trade