Washington, D.C., is enlisting Square Inc.’s help as its taxi commission tries to help the city’s cabbies compete with Uber drivers. By the end of August, all of the taxis in Washington have to tear out their traditional meters and start using smartphones or tablets, in what the city government has been describing as a complete reimagining of how the cab system works. On Wednesday, the Department of For-Hire Vehicles is announcing that Square will process the payments going through those mobile devices.For Square, the deal reflects an increasing focus on becoming the payment platform for a range of other company’s mobile applications, websites and point-of-sale devices. No money is changing hands between the company and the city. Square agreed to satisfy the department’s requirement that drivers give up no more than 2.65 percent of their fares in transaction fees, according to the department. That’s lower than the standard 2.75 commission it usually takes and significantly less than the 3.5 percent to 5 percent commission that drivers currently pay to use the mechanical meters, according to Ernest Chrappah, the director of the city’s taxi regulator. A spokesman for Square said it doesn’t comment on individual rates.