def round_ans(val, decimals=2):
    """
    Rounds the value to a specified number of decimal places.
    :param val: Number to be rounded
    :param decimals: Number of decimal places to round to (default is 1)
    :return: Rounded value as a string
    """
    return f"{val:.{decimals}f}"


def to_grams(to_convert):
    """
    Converts from Oz to G
    :param to_convert: Weight to be converted in Oz
    :return: Converted Weight in G or error if negative value
    """
    if to_convert < 0:
        return "Error: Weight cannot be negative"

    answer = to_convert * 28.35
    return round_ans(answer)


def to_ounces(to_convert):
    """
    Converts from G to Oz
    :param to_convert: Weight to be converted in G
    :return: Converted Weight in Oz or error if negative value
    """
    if to_convert < 0:
        return "Error: Weight cannot be negative"

    answer = to_convert / 28.35
    return round_ans(answer)


# Main routine / Testing starts here
if __name__ == "__main__":
    # Test Cases for Conversion Functions
    print("10 Oz to Grams:", to_grams(10))  # Converts 10 Oz to Grams
    print("100 Grams to Ounces:", to_ounces(100))  # Converts 100 Grams to Ounces
    print("Invalid Test (Negative Value -5 Oz):", to_grams(-5))  # Should return an error message
    print("Invalid Test (Negative Value -100g):", to_ounces(-100))  # Should return an error message