IMO.....only get a same size spare, if......you have a locker or spool in the rear axle, or.....you can get one cheap (I would not buy a new tire for a spare).

I have had wal-mart put 225/75s on my samurai and they didn't say a thing.....I don't know if their "book" says a 225 will fit (or is an acceptable tire size)....but I would assume it says"no".  I think it will depend on your wal-mart and who you are dealing with there.

Same problem with Sam's Club (Walmart Light).  Had four 225s off their rack in a cart.  They took my tires off the rims, then called and said they would only put 205's on the Tracker.  Told them to put my old tires back on.  Went directly across the street to NTB, no problem, and $40 less...