It turns out traditional grocery store food stocks like Kroger (NYSE: KR) and Albertsons (NYSE: ACI) are not faring so well against mass merchandisers such as Walmart (NYSE: WMT) and Target (NYSE: TGT). Online grocery sales plummeted over 12% in May compared to April as food prices soared by a similar amount, making this the fourth month out of the last five that they fell. The survey also noted that both grocery stores and mass merchandisers did see larger order values in the month, though that likely means they were buying bigger items, but fewer of them.