Hi Ton
For the Cart and Checkout, you can create/edit a custom display template and a data-bind="..." with a visible condition like this shown in red:
<div class="form-group rvdsf-label-totaltaxamount" data-bind="visible: SalesOrderSet.TotalTaxAmount() > 0" >
<label class="control-label col-xs-7">@Html.LocalizeString("TotalTaxLabel")</label>
<div class="col-xs-5">
<p class="form-control-static" data-bind="text: SalesOrderSet.FormattedTotalTaxAmount"></p>
</div>
</div>
For the Confirmation page, you can create/edit the custom display template and wrap the area with a Razor if condition:
@if (Model.SalesOrderSet.TotalTaxAmount > 0)
{
<div class="form-group rvdsf-label-totaltaxamount">
<label class="control-label col-xs-7">@Html.LocalizeString("TotalTaxLabel")</label>
<div class="col-xs-5">
<p class="form-control-static">@Model.SalesOrderSet.FormattedTotalTaxAmount</p>
</div>
</div>
}
Take a backup of your template first if you're not comfortable making changes. I hope this helps.