According to National Electrical Code, What is proper installation of grounded duplex receptacle, ground up or

down? Reason being, if metal cover plate is used and the single retaining screw backs out causing the metal recepatcle cover to rest on an energized hot and neutral plug which is not completely "pluged in" thus resulting in a electrical hazardous condition. Does the latest NEC Code state all duplex recptacles to now be installed with the ground up to prevent such an hazard from happening?