public static decimal ToUnit(decimal number, decimal unit, MidpointRounding mode)
        {
            if (unit > 1m) unit = 1m;

            string unitStr = unit.ToString();
            int decimals = 0;

            string separator = ThreadHelper.CurrentNumberFormat.NumberDecimalSeparator;
            int idx = unitStr.IndexOf(separator);
            if (idx >= 0)
            {
                bool nonZero = false;

                unitStr = unitStr.Substring(idx + separator.Length);
                foreach (char c in unitStr)
                {
                    if (c == '0' && nonZero) break;
                    if (c != '0') nonZero = true;
                    decimals++;
                }
            }

            number = decimal.Round(number, decimals, mode);

            decimal i = decimal.ToInt32(number);
            decimal f = (decimal)Math.Pow(10d, decimals);
            decimal d = (number - i) * f;
            decimal u = unit * f;

            number = i + (d - d % u) / f;
            
            return number;
        }

sub tounit($$) {
    # pick parameters
    my($num, $unit) = @_;

    # check parameters
    return undef unless looks_like_number($num);
    return undef unless looks_like_number($unit);
    return $unit unless $unit; # edit

    # round number
    my $res = $unit * sprintf( '%.0f', $num / $unit );

    # return rounded number
    return $res;
} # tounit

use POSIX qw(floor);
my $unit = 0.05;
my $number = 12.34567;
my $rounded = $unit * floor(0.5 + $number / $unit);

public static decimal ToUnit(decimal number, decimal unit, MidpointRounding mode)
{
    if (unit > 1m) unit = 1m;
    return unit * decimal.Round(number / unit, mode);
}