Is there customs value for international shipments?

Yes, there is. The total which is shown in the order is the total with tax only. Any additional payments collected by customs after shipment is not affiliated to Nice one.
You can check Aramex shipping charges below:
Kuwait:
Customs: 1 kd stamp+2 kd clearance charges +IATA charges* +5 percent cd of the total value of the shipment.
*IATA charges: depend on the weight and origin ,No vat applicable.
United Arab Emirates:
Invoice value with 991.72 AED and above subject to customs duty and VAT.
there is a VAT applicable between 100 AED and 999 AED.
Bahrain:
Above 301.68 BHD as total invoice value, will be 5% customs+ vat 5%.
 Oman:
To 299.15 OMR value shipments will be 5% on total invoice value + 3.47 OMR Clearance Fees Per Shipment. No Vat applicable.
In case the customs collected an amount on the shipment, contact ARAMEX 920027447 for any inquiry or clarification.