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function round2(x) {
    return Math.round(x * 100) / 100;
}

var totalAmounts = [];
var rate = TaxRate; //TaxRate is a local variable input (Scalar)

for (var i = 0; i < Subtotal.length; i++) {
    var sub = Subtotal[i]; //Subtotal[i] is context variable input (Array)
    var tax = round2(sub * rate);
    totalAmounts.push(round2(sub + tax));
}

var taxAmount = totalAmounts.length > 0 ? round2(Subtotal[0] * rate) : 0;

({
    TotalAmount: totalAmounts, //totalAmounts is a list (context variable output)
    TaxAmount: taxAmount //taxAmount is a scalar (local variable output)
});