ISSAQUAH, Wash. - Costco Wholesale Corporation (NASDAQ:COST), a retail giant with a market capitalization of $467 billion and an "GREAT" overall financial health score according to InvestingPro, disclosed its sales figures for the retail month of May, revealing a 6.8% increase to $20.97 billion from $19.64 billion in the same period last year. For the first 39 weeks of its fiscal year, the compa..