How to display price including tax with formatting?

Running any number through the function woocommerce_price() will format that number with the number of decimals, thousands separator, currency symbol and currency location chosen in the admin.

Add the function to your code snippet should format the price correctly:

<?php if ( $price_html = $product->get_price_including_tax() ): ?>
<span class="price"><?php echo woocommerce_price($price_html); ?></span>