First at All : ID MUST BE UNIQUE
Here is your working code : http://www.bootply.com/120472
HTML :
<ul class="nav nav-tabs">
<li class="active"><a href="#tab1" data-toggle="tab">Shipping</a></li>
<li><a href="#tab2" data-toggle="tab">Quantities</a></li>
<li><a href="#tab3" data-toggle="tab">Summary</a></li>
</ul>
<div class="tab-content">
<div class="tab-pane active" id="tab1">
<a class="btn btn-primary btnNext" >Next</a>
</div>
<div class="tab-pane" id="tab2">
<a class="btn btn-primary btnNext" >Next</a>
<a class="btn btn-primary btnPrevious" >Previous</a>
</div>
<div class="tab-pane" id="tab3">
<a class="btn btn-primary btnPrevious" >Previous</a>
</div>
</div>
JS :
$('.btnNext').click(function(){
$('.nav-tabs > .active').next('li').find('a').trigger('click');
});
$('.btnPrevious').click(function(){
$('.nav-tabs > .active').prev('li').find('a').trigger('click');
});
Snippet:
$('.btnNext').click(function(){
$('.nav-tabs > .active').next('li').find('a').trigger('click');
});
$('.btnPrevious').click(function(){
$('.nav-tabs > .active').prev('li').find('a').trigger('click');
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet" integrity="sha384-BVYiiSIFeK1dGmJRAkycuHAHRg32OmUcww7on3RYdg4Va+PmSTsz/K68vbdEjh4u" crossorigin="anonymous">
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js" integrity="sha384-Tc5IQib027qvyjSMfHjOMaLkfuWVxZxUPnCJA7l2mCWNIpG9mGCD8wGNIcPD7Txa" crossorigin="anonymous"></script>
<ul class="nav nav-tabs">
<li class="active"><a href="#tab1" data-toggle="tab">Shipping</a></li>
<li><a href="#tab2" data-toggle="tab">Quantities</a></li>
<li><a href="#tab3" data-toggle="tab">Summary</a></li>
</ul>
<div class="tab-content">
<div class="tab-pane active" id="tab1">
<a class="btn btn-primary btnNext" >Next</a>
</div>
<div class="tab-pane" id="tab2">
<a class="btn btn-primary btnNext" >Next</a>
<a class="btn btn-primary btnPrevious" >Previous</a>
</div>
<div class="tab-pane" id="tab3">
<a class="btn btn-primary btnPrevious" >Previous</a>
</div>
</div>