Change the way Amount is calculated in ERPNext Selling

sales_order_amt.js

// Replace with new calculation of item value
cur_frm.cscript.calculate_item_values = function() {
    var me = this;

    if (!this.discount_amount_applied) {
        $.each(this.frm.item_doclist, function(i, item) {
            frappe.model.round_floats_in(item);
            item.rate = flt(item.amount / item.qty, precision("rate", item));
            me._set_in_company_currency(item, "price_list_rate", "base_price_list_rate");
            me._set_in_company_currency(item, "rate", "base_rate");
            me._set_in_company_currency(item, "amount", "base_amount");
        });
    }
}

// Calculate back the price then update
cur_frm.cscript.custom_amount = function(doc, dt, dn) {
    var sales_order_item = locals[dt][dn];
    sales_order_item.rate = sales_order_item.amount/sales_order_item.qty;
    cur_frm.fixed_amt = true;
    cur_frm.cscript.calculate_taxes_and_totals();
}