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 $59.32   7.811%   $63.9535   $63.95   $63.95   $64.00  
  Purchase #2 $44.59   4.718%   $46.6938   $46.69   $46.70   $46.70  
  Purchase #3 $69.32   5.649%   $73.2359   $73.24   $73.25   $73.20  
  Purchase #4 $226.49   5.213%   $238.2969   $238.30   $238.30   $238.30  
  Purchase #5 $224.64   8.376%   $243.4558   $243.46   $243.45   $243.50  
  Purchase #6 $126.99   4.581%   $132.8074   $132.81   $132.80   $132.80  
  Purchase #7 $8.31   9.158%   $9.071   $9.07   $9.05   $9.10  
  7 purchase totals = $759.66       $807.5143   $807.52   $807.50   $807.60