Update your Button's click handler
<Button Click="Button_Click" />
Access Button's tag in code
private void Button_Click(object sender, RoutedEventArgs e)
{
var tag = (sender as Button).Tag;
//do tag dependent work
}
Side Note:
Button_click
is called for any button clicked inside your data-binding but sender will be the specific instance of the clicked button that's why you can access all of its properties.