This year, Costco raised its annual membership fees 10 percent in Taiwan, Korea, Japan, Mexico and the U.K. In the U.S., the warehouse club has traditionally pushed rates up every five years or so. The fifth anniversary of the last increase will occur next month. While the company isn’t divulging its plan yet, CFO Richard Galanti said recently that the company would be more apt to impose the increase if same-store sales were a “little weaker.”