gettext filter not working for woocommerce

I want the theme to display GST instead of VAT. Searched everywhere, found a gettext filter. But doesn't work for me. Would you please spread some light?. I don't want to use any plugins. Below is the code that I have tried.

add_filter( 'gettext', function( $translation, $text, $domain ) {
if ( $domain == 'woocommerce' ) {
if ( $text == '(incl. VAT)' ) { $translation = '(incl. GST)'; }
}
return $translation;
}, 10, 3 );

All this is needed for the Checkout Page only. The SubTotal and Individual prices are shown in VAT and the Total is shown in GST as per the tax slabs.