Example of how to include a 'SubTotal', 'Taxable SubTotal' and 'Tax Total' column to the registration CSV report.

tw_ee_add_additional_finance_columns.php

<?php //Please do not include the opening PHP tag if you already have one.

add_filter(
    'FHEE__EventEspressoBatchRequest__JobHandlers__RegistrationsReport__reg_csv_array',
    'tw_ee_add_additional_finance_columns',
    10,
    2
);
function tw_ee_add_additional_finance_columns( $reg_csv_array, $reg_row ) {
    $registration = EEM_Registration::instance()->get_one_by_ID( $reg_row['Registration.REG_ID'] );
    if( $registration instanceof EE_Registration && $registration->is_primary_registrant() ) {
        $grand_total = EEM_Line_Item::instance()->get_one(
            array(
                array(
                    'TXN_ID' => $reg_row['TransactionTable.TXN_ID'],
                    'LIN_type' => EEM_Line_Item::type_total
                )
            )
        );

        // Sub Total
        $items_total = $grand_total->get_items_total();
        
        // Taxable total
        $taxable_total = $grand_total->taxable_total();

        // Tax Total
        $tax_total = $grand_total->get_total_tax();

        $reg_csv_array[ __( 'SubTotal', 'event_espresso' ) ] = $items_total;
        $reg_csv_array[ __( 'Taxable SubTotal', 'event_espresso' ) ] = $taxable_total;
        $reg_csv_array[ __( 'Tax Total', 'event_espresso' ) ] = $tax_total;
    }   
    return $reg_csv_array;
}