How do I Make Totals Appear on the Last Page Only?

The simplest way to make totals appear on only the last page of the document is to place the total placeholders in the body of the document rather than in the footer of the document.  The footer will normally repeat for each page of the document whereas if you simply place your totals in the body of the document, after the repeating placeholders, then they will naturally appear on the last page only.  There are other ways in OpenOffice/LibreOffice to use firstpage and lastpage styles to achieve the totals on last page effect, but placing the totals within the body after the repeating tags is the simplest.