double相乘有关问题

double相乘问题
double b = 100;
double c = 2.999999;
BigDecimal b1 = new BigDecimal(b);
BigDecimal b2 = new BigDecimal(c);
BigDecimal b3 = b1.multiply(b2);
double d = b3.setScale(2, BigDecimal.ROUND_HALF_UP).doubleValue();