You are trying to achieve something that looks like this:
Please perform the actions below in order to get delineated columns in the data-view created by the List Rollup Web Part.
1) First go to the edit button at the top right of your view.
2) From there, got to Modify Shared Web Part, XLS editor, as pictured below:
This should open an editable notepad window, allowing you to add a border, distinguishing your columns.
In the notepad, under $dvt_grouptype, find the <td class="ms_vb2"> sections for each column displayed in the Data View and add Style="border-right:2px solid black" after the <td class="ms_vb2"> text as demonstrated:
Save your changes and you should have something that looks like the first picture.
Please let us know if you have any questions or concerns.