JSFiddle - React, Tailwind, and code Playground

HTML

<select class="sel">
  <option value="volvo">Volvo</option>
  <option value="saab">Saab</option>
  <option value="mercedes">Mercedes</option>
  <option value="audi">Audi</option>
</select>
<table>
    <tr>
        <th>Product</th>
        <th class="priceheader" data-taxstate="n">Price (€)</th>
    </tr>
    <tr>
        <td>Apple</td>
        <td class="price">10</td>
    </tr>
    <tr>
        <td>Banana</td>
        <td class="price">5</td>
    </tr>
    <tr>
        <td>Orange</td>
        <td class="price">12</td>
    </tr>
</table>

JavaScript

tax = "1.0" //20%
$( ".sel" ).change(function() {
  var veiculo = $( ".sel" ).val();
	if(veiculo == "saab"){
  	tax = "1.0";
  }else if(veiculo == "mercedes"){
  	tax = "1.05";
  }else if(veiculo == "audi"){
  	tax = "1.1";
  }
  if ($(".priceheader").attr("data-taxstate") == "n") {
      $(".price").each(function () {
          $(this).html(parseFloat($(this).html()) * tax);
      });
      $(".priceheader").attr("data-taxstate", "y");
  }
});