JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" id="textbox" placeholder="insert number to round" onChange="calculate(1)" />
<input type="text" id="textboxOut" placeholder="output" disabled/>

JavaScript

function calculate() {
  var num = parseFloat(document.getElementById('textbox').value); // Read Value from DOM
  var rounded = num.toFixed(2); // Round Number
  document.getElementById('textboxOut').value = rounded; // Output Result
}