woocs_woocommerce_variation_prices
Works in index.php -> public function woocommerce_variation_prices -> can be used for any manipulations with variable prices, for example rounding of them. Add next code in functions.php of your current wp theme:
Example:
add_filter('woocs_woocommerce_variation_prices', function($price) {
return round($price * 2, 0) / 2;
});