docs: public BigMoney plusRetainScale(double amountToAdd, RoundingMode roundingMode) {
          if (amountToAdd == 0) {
              return this;
          }
          BigDecimal newAmount = amount.add(BigDecimal.valueOf(amountToAdd));
          newAmount = newAmount.setScale(getScale(), roundingMode);
          return BigMoney.of(currency, newAmount);
      }