BigDecimal x = new BigDecimal("45.457");
x = x.setScale(2, BigDecimal.ROUND_HALF_UP); /* 2 - количество знаков после запятой */

System.out.println("x = " + x.doubleValue());  

BigDecimal bigDecimal = new BigDecimal("45.457");
bigDecimal = bigDecimal.setScale(3, [roundingMode]);
System.out.println(bigDecimal.doubleValue());

import java.math.BigDecimal;


public class RoundDown
{

  public RoundDown()
  {
  }

  public static double roundDownScale2(double aValue)
  {
    BigDecimal decimal = new BigDecimal(aValue);
//    decimal = decimal.setScale(10,BigDecimal.ROUND_UP);
    decimal = decimal.setScale(2,BigDecimal.ROUND_DOWN);
    double result = decimal.doubleValue();
    return result;
  }

  public static void main(String[] args)
  {
    double value = 28.68d;
    double valueRounded = roundDownScale2(value);
    System.out.println("value = " + value);
    System.out.println("valueRounded = " + valueRounded);

    value = 28.681d;
    valueRounded = roundDownScale2(value);
    System.out.println("value = " + value);
    System.out.println("valueRounded = " + valueRounded);
    
  }
  
}

		BigDecimal d = new BigDecimal(1.555);
		System.out.println(d);
		System.out.println(d.setScale(2, RoundingMode.HALF_UP));

		BigDecimal d = new BigDecimal(1.5550000000001);
		System.out.println(d);
		System.out.println(d.setScale(2, RoundingMode.HALF_UP));

String str = Double.valueOf(1.555).toString();
BigDecimal d = new BigDecimal(str);
System.out.println(d.setScale(2, RoundingMode.HALF_UP));

результат: 1.56