banking_dispenser.csx

var rarity = new [] { 5000, 2000, 1000, 500, 100 };
int[] dispenser_action(int sum)
{
    if (sum % rarity.OrderBy(x => x).First() != 0)
        throw new Exception();
    var result = new List<int>();
    foreach (var r in rarity)
    {
        var x = (sum - (sum % r)) / r;
        result.AddRange(Enumerable.Range(0, x).Select(_ => r));
        sum -= r * x;
        if (sum == 0) break;
    }
    return result.ToArray();
}