fun Double.round(decimals:Int)

DoubleExt.kt

// see discussion on alternatives here: https://discuss.kotlinlang.org/t/how-do-you-round-a-number-to-n-decimal-places/8843/15

fun Double.round(decimals:Int, roundingMode:RoundingMode=RoundingMode.HALF_EVEN):Double =
    toBigDecimal().setScale(decimals, roundingMode).toDouble()
    
# ???    
fun Double.round2(decimals: Int): Double {
    val locale:Locale = Locale.US
    val aTxt:String = String.format(locale, "%.${decimals+1}f", this)
    val aDouble:Double = aTxt.toDouble()
    val bTxt:String = String.format(locale, "%.${decimals}f", aDouble)
    return bTxt.toDouble();
}