groovy script to map tax amount from order management to subscription management

We are trying to map the estimated tax for the order(ChargeCurrencyExtendedAmount_Custom)to the subscription estimated tax(EstimatedTax_Custom)at the product level with the groovy script below. We are unable to see any value populate at OOB Standard estimated tax field in subscription.

if (OrderChargeComponents.OrderChargeComponentPriceElementCode == 'QP_EXCLUSIVE_TAX'){
SubProd.EstimatedTax_Custom = sum(OrderChargeComponents.ChargeCurrencyExtendedAmount_Custom)
}

 Could you please help us with groovy script to map the above two fields. We are expecting total 8+1.6 estimated tax in subscription. We did service mappings and added in alogrithm.