[Technical] want to use the blockchain as public entropy machine

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Is there a way to get the latest global transaction hash?  I basically want to use the blockchain as some sort of global publicly accessible entropy device.  I am creating a gambling site and need a better way to show people the site is transparent.  I will use that entropy to decide card shuffles, roulette rolls and whatnot.  Solved hashes come every few minutes so it's not as useful for realtime results. 

I am not new to bitcoin but am new to the technical side,  any help would be appreciated.  Or if you have a better suggestion I would appreciate that as well.