Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $136.35   11.454%   $151.9675   $151.97   $151.95   $152.00  
  Purchase #2 $7.77   12.671%   $8.7545   $8.75   $8.75   $8.80  
  Purchase #3 $59.99   7.436%   $64.4509   $64.45   $64.45   $64.50  
  Purchase #4 $245.91   11.859%   $275.0725   $275.07   $275.05   $275.10  
  Purchase #5 $76.83   13.462%   $87.1729   $87.17   $87.15   $87.20  
  Purchase #6 $105.40   12.697%   $118.7826   $118.78   $118.80   $118.80  
  Purchase #7 $246.62   8.655%   $267.965   $267.97   $267.95   $268.00  
  7 purchase totals = $878.87       $974.1659   $974.16   $974.10   $974.40