JSFiddle - React, Tailwind, and code Playground

HTML

<span id="cena_aktualna">0.00</span>
<a href="#" id="gruszki">Add!</a>

JavaScript

$(function() {
 $('a#gruszki').click(function() { 
 var cena_poczatkowa = parseFloat($("#cena_aktualna").text());
 var cena_dodana = (cena_poczatkowa + 1.01).toFixed(4);
 $("span#cena_aktualna").text(cena_dodana);
    });

});