JSFiddle link forked from yours.
Check and let me know if it works. However you might find alignment issues.
CSS
.scrollit {
overflow: scroll;
height: 100px;
}
HTML
<table border="1">
<thead>
<tr class="tableHeading">
<th width="10%">Description</th>
<th width="5%">Pack</th>
<th width="5%">size</th>
<th width="7%">Vendor Item Code #</th>
<th width="12%">UPC #</th>
<th width="9%">Item Quantity</th>
<th width="9%">Previous
<br>Item Quantity</th>
<th width="8%">% Variance
<br>Quantity Count</th>
<th width="7%">Unit Cost</th>
<th width="10%">Total Cost</th>
<th width="10%">Previous Cost</th>
<th width="8%">% Variance
<br>Cost</th>
</tr>
</thead>
<tbody>
<tr>
<td colspan="12">
<div class="scrollit">
<table>
<tr class="">
<td width="10%">TOSTADA CASERA TRANSFERS</td>
<td width="5%">1</td>
<td width="5%">24 CNT</td>
<td width="7%">658978990552</td>
<td width="12%" style="width: 7%; overflow: hidden;">748703800199</td>
<td width="9%" id="quantity" data-itemid="905">56565</td>
<td width="9%">0</td>
<td width="8%">100</td>
<td width="7%">$0.68</td>
<td width="10%">$0.00</td>
<td width="10%">$0.00</td>
<td width="8%">0</td>
</tr>
<tr class="">
<td width="10%">KING SIZE COMO HECHAS A MANO TRANSFE</td>
<td width="5%">1</td>
<td width="5%">1 CNT</td>
<td width="7%">658978991952</td>
<td width="12%">748703800335</td>
<td width="9%" id="quantity" data-itemid="919">0</td>
<td width="9%">0</td>
<td width="8%">0</td>
<td width="7%">$0.98</td>
<td width="10%">$0.00</td>
<td width="10%">$0.00</td>
<td width="8%">0</td>
</tr>
</table>
</div>
</td>
</tr>
</tbody>
</table>