BigDecimal.ROUND

四舍六入，五看前一位是偶数舍，奇数进位

BigDecimal a = new BigDecimal(5.54); System.out.println(a.setScale(1, BigDecimal.ROUND_HALF_EVEN));

5.54 5.5 2.55 2.6 1.66 1.7 1.25 1.2 1.06 1.1 -1.06 -1.1 -1.11 -1.1 -1.65 -1.6 -2.55 -2.6 -5.54 -5.5