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 $90.67   8.283%   $98.1802   $98.18   $98.20   $98.20  
  Purchase #2 $112.63   3.179%   $116.2105   $116.21   $116.20   $116.20  
  Purchase #3 $51.45   13.564%   $58.4287   $58.43   $58.45   $58.40  
  Purchase #4 $179.57   8.218%   $194.3271   $194.33   $194.35   $194.30  
  Purchase #5 $57.39   3.874%   $59.6133   $59.61   $59.60   $59.60  
  Purchase #6 $227.99   5.569%   $240.6868   $240.69   $240.70   $240.70  
  Purchase #7 $44.78   13.346%   $50.7563   $50.76   $50.75   $50.80  
  7 purchase totals = $764.48       $818.2029   $818.21   $818.25   $818.20