By Elvina Nawaguna WASHINGTON (Reuters) – The U.S. Postal Service narrowed losses in its latest quarter, as a surge in online shopping and package delivery boosted revenues during the busy holiday season. Revenues from shipping and package delivery rose by 14.1 percent to $479 million, driven by growth in online shopping and a lucrative deal with online retail giant Amazon to deliver packages on Sundays in some U.S. cities, the agency said on Friday. The Postal Service has been grappling with tumbling mail volumes as Americans communicate more online, and as massive payments for its future retirees’ health benefits take a toll. A 2006 law requires the Postal Service to fund 75 years worth of its future retirees’ healthcare by 2016.