Scala implementation of Roman Numeral conversion

RomanNumeral.scala

class RomanNumeral {
  def toRomanNumerals( number: Int) : String = {
    toRomanNumerals( number, List( ("M", 1000),("CM", 900), ("D", 500), ("CD", 400), ("C", 100), ("XC", 90),
                                   ("L", 50), ("XL",40), ("X", 10), ("IX", 9), ("V", 5), ("IV", 4), ("I", 1) ))
  }

  private def toRomanNumerals( number: Int, digits: List[(String, Int)] ) : String = digits match {
    case Nil => ""
    case h :: t => h._1 * ( number / h._2 ) + toRomanNumerals( number % h._2, t )
  }
}