Why Does My Car Roll A Little, About Ten Inches, After I Put It In Park?

A small amount of movement is acceptable but no where near the amount your talking (1-2 inch could be considered ok) as the transmission locks itself with the power train, I'd suggest getting yourself a transmission service to check the gears themselves to make sure there isn't an excessive amount of play with the gears or connections to the engine/drive train

This happens in almost every car with an auto box.  When you select 'Park' on the gear shift, it is just the movement until the car actually finds 'Park'.  It is outside the normal gear box range, and it just has to find it.  Not a big problem but always allow for this forward motion when parking.