I'd go with Moss' call on genus Lepiota. The second photo is just enough out-of-focus to make it impossible for me to call it as L. acutesquamosa, which is the one with pyramidal scales on top of the cap. The latter is an edible. I hasten to say that there are lethal Lepiota's out there. The spore print suggestion by altissimus is also right on the money. Genus Chlorophyllum looks very similar but has green rather than white spores...and is toxic.
Personally, I don't collect Lepiota's for eating except for L. procera, the classic parasol....it's tough when a genus has both lethal and choice eating mushrooms!
Field guides often put these and the toxic Amanita's together. They are not closely related genetically, but newbies can confuse them. Key differences are the swollen and usually sack-like bases of the Amanita and rounded base of the stipe (or stem) of the Lepiota's. Once again, also a quick call with a microscope. The hyphae in the "meat" of the cap are interwoven in Lepiota while they are divergent in Amanita.
If all of the above is too much, stick with the grocery store.