Skittels--In case you don't know, there is a hack you can apply that will allow you to do just that (fully power down by holding down the "enter" button for five seconds).
It was posted here by JS Wolf:
https://www.mobileread.com/forums/showthread.php?t=23143
Great hack! Also adds a clock to the page number bar, nicer icons, and same size fonts in the menus. Makes my 505 look much nicer!
Be aware that if you do this it will take awhile for your reader to boot back up next time you turned it on.
dordale