CENTENNIAL, Colo. — The City of Centennial turned 25 this year. While plenty has changed over the last two decades, two things have stayed the same: the 2.5% sales tax rate, one of the lowest in the region, and the fact that the city has never taken on any debt. "We save our money until we're able to do projects," said Mayor Christine Sweetland, who was sworn into office in January after spending years on city council.