Round VAT total to .X5

Add the following code to the functions.php of your child-theme (download a free blank child-theme here).

function euro_5cent_rounding( $in ) {
    return round( $in / 5, 2 ) * 5;
  }
  add_filter( 'woocommerce_tax_round', 'euro_5cent_rounding' );
function get_taxes_euro_5cent_rounding( $taxes ) {
return array_map( 'euro_5cent_rounding', $taxes );
}
add_filter( 'woocommerce_cart_get_taxes', 'get_taxes_euro_5cent_rounding' );

 
Then, empty the WooCommerce caches in order to see the changes.

Source: https://wordpress.org/support/topic/round-vat-total-to-x0?replies=6#post-8357651