The retail titan's sales are growing at an impressive clip.Shares of Costco Wholesale (COST +3.74%) rose on Thursday, following the release of the warehouse retailer's December sales figures. By the close of trading, Costco's stock price was up more than 3% after rising as much as 5.6% earlier in the day. Business is boomingCostco's net sales jumped 8.5% year over year to $29.86 billion for the five weeks ended Jan. 4.Excluding the impacts from fluctuations in gasoline prices and foreign exchange rates, the ...