You don't have to own a high-flying technology business to achieve magnificent returns in the stock market. Even boring retailers can boost your portfolio. That's certainly true for Costco Wholesale (COST -0.47%). Shares of the popular warehouse store operator are up 219% just in the past five years. Looking ahead, can this phenomenal retail stock double your money in the next five years? Here's what investors should be thinking about right now. Costco is a fantastic business If we just look at Costco's und ...