DouKaku?

fun includeTax str =
let
  val s = tokens "[0-9]+" str
  val yen = tokens "[^0-9]+" str
  val tax = map (fn x => itoa (atoi x * 105 div 100)) yen

  fun loop (a::a', b::[]) = a ^ b ^ (concat a')
    | loop (a::a', b::b') = a ^ b ^ (loop (a', b'))
in
  loop (s, tax)
end