Produkte ab dem 10 Stück nur noch in 10er Schritten

add_filter( 'woocommerce_quantity_input_args', 'mmx_change_qty_conditional', 20, 2 );
function mmx_change_qty_conditional( $args, $product ) {
	global $woocommerce;
	$items = $woocommerce->cart->get_cart();
	foreach( $items as $cart_item_key => $cart_item_values ){
		if ( ! is_cart() && $cart_item_values['product_id'] == $product->id && $cart_item_values['quantity'] >= 10 ) {
			$args['input_value']        = 10;   // Starting value
			$args['max_value']          = 20;   // Maximum value
			$args['min_value']          = 10;   // Minimum value
			$args['step']               = 10;   // Quantity steps
			return $args;
		}
	}
	return $args;
}