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 $59.92   10.490%   $66.2056   $66.21   $66.20   $66.20  
  Purchase #2 $110.62   9.632%   $121.2749   $121.27   $121.25   $121.30  
  Purchase #3 $92.44   11.340%   $102.9227   $102.92   $102.90   $102.90  
  Purchase #4 $95.36   10.681%   $105.5454   $105.55   $105.55   $105.50  
  Purchase #5 $189.45   4.204%   $197.4145   $197.41   $197.40   $197.40  
  Purchase #6 $92.83   3.211%   $95.8108   $95.81   $95.80   $95.80  
  Purchase #7 $219.54   8.231%   $237.6103   $237.61   $237.60   $237.60  
  7 purchase totals = $860.16       $926.7842   $926.78   $926.70   $926.70