WIESBADEN, Germany — Overseas military customers ordering gifts online from certain retailers might get an unpleasant surprise when shipping and handling fees are tacked on at the end of the purchase. Those same customers might be most surprised to find that retail giant Walmart had the biggest markup. On a $120 purchase, Walmart.com charged $10.35 to ship to an APO address, compared with $2.10 to a stateside address. For most items, Amazon.com charged the same to ship to an APO address as a stateside address. And Target offered shipping on a $120 purchase to an APO address for less than...