If it is a real quarter, it could be quite valuable. However, it may be a fake designed to fool others when calling heads or tails on a coin flip. If you believe it is real, take it to a coin shop and ask for an expert opinion.
Quarters are generally not worth much at all, and I've never heard of a collectible quarter with two tails, can't find any information on one, I suspect it's not real.
A quarter that has two tails instead of a head and a tail is most likely a coin used in magic tricks or by someone that uses it to win a bet by flipping the coin and calling out heads. So the monetary value would be 0.
Theres almost a 99% chance its a novelty coin. However if it was real (only 3 known in existence as a mint error) then it would be worth atleast 100,000 dollars.