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 $61.67   6.181%   $65.4818   $65.48   $65.50   $65.50  
  Purchase #2 $143.45   7.143%   $153.6966   $153.70   $153.70   $153.70  
  Purchase #3 $51.76   9.574%   $56.7155   $56.72   $56.70   $56.70  
  Purchase #4 $146.75   3.814%   $152.347   $152.35   $152.35   $152.30  
  Purchase #5 $234.54   4.109%   $244.1772   $244.18   $244.20   $244.20  
  Purchase #6 $97.71   7.131%   $104.6777   $104.68   $104.70   $104.70  
  Purchase #7 $86.43   7.105%   $92.5709   $92.57   $92.55   $92.60  
  7 purchase totals = $822.31       $869.6667   $869.68   $869.70   $869.70