Here's a patch that shows one way of making a solid Total line. It's a bit of cop-out because, rather than attempting to span columns, it's highlighting all cells on rows that contain "Total:".

@@ -47,6 +47,7 @@
 foreach my $row ( @{$some_data} )    
 {
 my $k = 0;
+my $is_total_line = grep {$_ eq 'Total:'} @$row;
     foreach my $cell ( @{$row} )
     {
 
@@ -67,7 +68,7 @@
                                     font_color       => '#4D4D4D', #
                                     justify => "left",
                                 };
-        }elsif ( ($cell eq 'Total:') ){
+        }elsif ( $is_total_line ){
 
           $cell_props->[$j]->[$k] = {
                                     background_color => '#FFCA00', #
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