Help with parseInt() issue

Something off is happening with parseInt where for some reason it sometimes rounds the number up from a decimal, and sometimes it doesn’t. I can’t seem to find the cause of this behavior. Any ideas?

var unitToggle = document.querySelector('#toggle');
var wUnit = document.querySelector('#unit');
unitToggle.addEventListener("click", toggleUnits);

function toggleUnits(){
  if(wUnit.innerHTML == "C"){
    var oldTemp = parseInt(wTemp.innerHTML, 10),
        newTemp = oldTemp * 9 / 5 + 32;
    wTemp.innerHTML= newTemp;
    wUnit.innerHTML = "F";
    unitToggle.innerHTML ="Switch to Celsius";
  }else{
    var oldTemp = parseInt(wTemp.innerHTML, 10),
        newTemp = (oldTemp-32) * 5 / 9;
    wTemp.innerHTML= newTemp;
    wUnit.innerHTML = "C";
    unitToggle.innerHTML ="Switch to Fahrenheit";
  }
}

CodePen: https://codepen.io/abenjamin/pen/ZojJLq