JSFiddle - React, Tailwind, and code Playground

HTML

<form id="menu4strombolis">input1
    <input type="radio" name="menu1" value="5">
    <br>input2
    <input type="radio" name="menu2" value="10">
    <br>input3
    <input type="radio" name="menu3" value="15">
    <br>input4
    <input type="radio" name="menu4" value="20">
    <br>input5
    <input type="radio" name="menu5" value="25">
    <br>input6
    <input type="radio" name="menu6" value="30">
    <br>input7
    <input type="radio" name="menu7" value="35">
    <br>
</form>
<button id="getTotal">Total</button>
<div id="subtotal">Sub-Total:</div>
<div id="tax">Tax:</div>
<div id="total">Total:</div>

JavaScript

var button = document.getElementById("getTotal");

button.onclick = function () {
    var subtotalField = document.getElementById("subtotal");
    var radios = document.forms["menu4strombolis"].getElementsByTagName("input");
    var subtotal = 0;
    var tax = 0;
    var total = 0;

    for (var i = 0, length = radios.length; i < length; i++) {
        if (radios[i].checked) {
            subtotal += parseInt(radios[i].value);
        }
    }

    tax = (subtotal * .07).toFixed(2);;
    total = subtotal + tax;

    document.getElementById("subtotal").innerHTML = "Sub-Total: $" + subtotal;
    document.getElementById("tax").innerHTML = "Tax: $" + tax;
    document.getElementById("total").innerHTML = "Total: $" + total;
};