Yes, CLOSES is a Scrabble word!

Letter values in Scrabble US: C 3, L 1, O 1, S 1, E 1, S 1.

Is it a valid word?

CLOSES is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

move so that an opening or passage is obstructed; make shut
become closed
cease to operate or cause to cease operating
finish or terminate (meetings, speeches, etc.)
come to a close
complete a business deal, negotiation, or an agreement
be priced or listed when trading stops
engage at close quarters
cause a window or an application to disappear on a computer desktop
change one's body stance so that the forward shoulder and foot are closer to the intended point of impact
come together, as if in an embrace
draw near
bring together all the elements or parts of
bar access to
fill or stop up
unite or bring into contact or bring together the edges of
finish a game in baseball by protecting a lead

Also: stopping point, closing curtain, close up, shut down, close down, come together, fill up.