Open source code for Sales Tax Calculator on https://gauravtiwari.org/apps/sales-tax-calculator/

Sales Tax Calculator.html

<form id="salesTaxCalculator" class="block-half has-border">
        <div class="form-group my-3">
            <label class="form-check form-check-inline">
                <input class="form-check-input" type="radio" name="taxType" value="exclusive">
                <span class="form-check-label">Tax Exclusive</span>
            </label>
            <label class="form-check form-check-inline">
                <input class="form-check-input" type="radio" name="taxType" value="inclusive">
                <span class="form-check-label">Tax Inclusive</span>
            </label>
        </div>
        <div class="form-group mb-3">
            <label class="form-label">Amount</label>
            <input type="number" id="amount" class="form-control" required>
        </div>
        <div class="form-group mb-3">
            <label class="form-label">Sales Tax Rate</label>
            <div class="input-group box-lr">
                <input type="number" step="any" id="rate" class="form-control" required>
                <span class="input-group-text">%</span>
            </div>
        </div>
        <div class="form-group mb-3 text-center">
            <button type="button" class="btn btn-info" onclick="calculateTax()">Calculate</button>
            <button type="button" class="btn btn-lime" onclick="sampleInput()">Sample</button>
            <button type="button" class="btn btn-warning" onclick="resetForm()">Reset</button>
        </div>
        <div class="form-group box-lr">
            <label class="form-label">Calculated Tax:</label>
            <div id="calculatedTax"></div>
        </div>
    </form>
    <script>
        function calculateTax() {
    var amount = parseFloat(document.getElementById('amount').value);
    var rate = parseFloat(document.getElementById('rate').value) / 100;
    var taxType = document.querySelector('input[name="taxType"]:checked').value;
    var calculatedTax;

    if (taxType === 'exclusive') {
        calculatedTax = amount * rate;
    } else {
        calculatedTax = amount - (amount / (1 + rate));
    }

    document.getElementById('calculatedTax').innerText = '$' + calculatedTax.toFixed(2);
}

function sampleInput() {
    document.getElementById('amount').value = '100';
    document.getElementById('rate').value = '8';
    document.querySelector('input[name="taxType"][value="exclusive"]').checked = true;
}

function resetForm() {
    document.getElementById('salesTaxCalculator').reset();
    document.getElementById('calculatedTax').innerText = '';
}
    </script>
    <style>
        /* Add your CSS styling here */
        .form-group {
            margin-bottom: 15px;
        }
        .input-group-text {
            background-color: #e9ecef;
            border: 1px solid #ced4da;
            border-radius: 0.25rem;
            padding: 0.375rem 0.75rem;
        }
        .form-control {
            display: block;
            width: 100%;
            padding: 0.375rem 0.75rem;
            font-size: 1rem;
            line-height: 1.5;
            color: #495057;
            background-color: #fff;
            background-clip: padding-box;
            border: 1px solid #ced4da;
            border-radius: 0.25rem;
        }
        .btn {
            display: inline-block;
            font-weight: 400;
            text-align: center;
            vertical-align: middle;
            user-select: none;
            border: 1px solid transparent;
            padding: 0.375rem 0.75rem;
            font-size: 1rem;
            line-height: 1.5;
            border-radius: 0.25rem;
            transition: color 0.15s ease-in-out, background-color 0.15s ease-in-out, border-color 0.15s ease-in-out, box-shadow 0.15s ease-in-out;
        }
        .btn-info {
            color: #fff;
            background-color: #17a2b8;
            border-color: #17a2b8;
        }
        .btn-lime {
            color: #fff;
            background-color: #22a340;
            border-color: #22a340;
        }
        .btn-warning {
            color: #212529;
            background-color: #ffc107;
            border-color: #ffc107;
        }
    </style>