The game released on October 5th, 2010 but didn't manage to crack the top 10 in sales for that month (as far as NPD's). On November 22nd Konami reported that 1 million units had been
shipped between the US and Europe and that they were "extremely pleased at the positive response seen."
They also had this to say about the sales: "the remarkable sales achieved in such a short time are a true testament of the work and dedication that went into this project."
Source:
http://www.joystiq.com/2010/11/22/konami-ships-1-million-castlevania-lords-of-shadow-copies/
So I would guess that the game has sold somewhere in the neighborhood of 1 million copies by now, although that's just me speculating based on this information. Regardless, I think we can anticipate a sequel.