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 $61.53   7.695%   $66.2647   $66.26   $66.25   $66.30  
  Purchase #2 $204.81   9.611%   $224.4943   $224.49   $224.50   $224.50  
  Purchase #3 $46.49   6.725%   $49.6165   $49.62   $49.60   $49.60  
  Purchase #4 $62.47   7.130%   $66.9241   $66.92   $66.90   $66.90  
  Purchase #5 $97.93   10.709%   $108.4173   $108.42   $108.40   $108.40  
  Purchase #6 $140.27   12.549%   $157.8725   $157.87   $157.85   $157.90  
  Purchase #7 $225.92   11.413%   $251.7042   $251.70   $251.70   $251.70  
  7 purchase totals = $839.42       $925.2936   $925.28   $925.20   $925.30