Called an office with multiple people working here. When I answered, there was an automated message saying something like "you have been audited and the IRS has found a problem with your taxes" to please call back to get the matter straightened out. the number given to call back was the same number on the caller id. After seeing the responses here, I did not try to call back :).
Since that is a Washington, DC number you should call them back and mess with them. The Federal Government closed all DC area offices at noon local time due to the approaching blizzard. These foreign scammers are unlikely to be aware of that. You could express surprise that they are still in their office and hope they don't get trapped there by the snow or worse get stuck on the way home and freeze to death.
I received a call from this number but no one spoke. When I called back from a hardline someone with an Indian accent answered identifying himself as the Internal Revenue Service. As soon as I asked to confirm the number the person hung up on me.
Received a call saying something about tax fraud and misconduct. Called this number back and the automated message said: " This call cannot be completed as dialed!" then another sound after that, like a fax machine sounds when you call a phone number that is connected to one.