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 $72.56   12.581%   $81.6888   $81.69   $81.70   $81.70  
  Purchase #2 $104.57   9.626%   $114.6359   $114.64   $114.65   $114.60  
  Purchase #3 $239.31   11.429%   $266.6607   $266.66   $266.65   $266.70  
  Purchase #4 $45.50   3.629%   $47.1512   $47.15   $47.15   $47.20  
  Purchase #5 $187.55   4.172%   $195.3746   $195.37   $195.35   $195.40  
  Purchase #6 $128.52   6.484%   $136.8532   $136.85   $136.85   $136.90  
  Purchase #7 $87.58   6.789%   $93.5258   $93.53   $93.55   $93.50  
  7 purchase totals = $865.59       $935.8902   $935.89   $935.90   $936.00