code: @Override
      public NumberValue round(MathContext mathContext) {
          if (this.number instanceof BigDecimal) {
              return new DefaultNumberValue(((BigDecimal) this.number).round(mathContext));
          }
          return new DefaultNumberValue(new BigDecimal(this.number.toString()).round(mathContext));
      }
docs: /*
  (non-Javadoc)
  @see javax.money.NumberValue#round(java.math.MathContext)