WASHINGTON—The U.S. job market is booming and workers’ paychecks are growing thanks to a tax cut and raises. But Americans hunkered down on spending last month, a puzzle for an economy that leans heavily on their willingness to consume.

Sales at U.S. retailers fell 0.1% in February, marking a three-month slide. Much of the decline was tied to lower sales of cars and weak gasoline prices. Americans also reduced shopping for furniture, health products, groceries and electronics.

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