How can I add numbers as in a shopping cart in javascript and display them properly with the numbers after the decimal points

please help me, in JavaScript how can I add multiple numbers as like in an ecommerce shopping cart and display the numbers after the decimal point properly? If the attribute value data-price is 2.50, I would like to display the value as 2.50 on the balance.innerHTML, not as 2.5 as it appears. Here is my code:

  <div class="row">

  <div class="col6">
  2,50$
  <div  onclick="addC(this)" data-price="2.50">
  Add to cart
  </div>
  </div>


  <div class="col6">
  2,40$
 <div onclick="addC(this)" data-price="2.40">
 Add to cart
 </div>
 </div>

 </div>

 <div id="balance" data-price="0">0</div>

function addC(product){

let balance = document.getElementById('balance');

balance.innerHTML = parseFloat(Number(balance.innerHTML).toFixed(2)) + parseFloat(Number(product.getAttribute('data-price')).toFixed(3));

}

In this method, can you please tell me, since I am using numbers with decimal points, how can I show them with the zeros, two digits after the decimal point. I want to display them as 2,50 and 2,40 and sum them, but the current output is 2.5 and 2.4 on the DOM:

Use toFixed on the final sum rather than on the addends.

(2.4 + 2.5).toFixed(2)  --> yields "3.30"