You need to first register the style and then en-queue it! This might work!
function custom_style_method() {
wp_register_style( 'paralax_style', get_template_directory_uri().'/paralax.css' );
}
add_action('wp_enqueue_scripts', 'custom_style_method');
add_filter( 'template_include', 'themename_include_page_specific_css', 1000 );
function themename_include_page_specific_css( $template ){
if ( is_page_template('single-location.php' ) ) {
wp_enqueue_style( 'paralax_style' );
}
return $template;
}