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 $95.44   4.209%   $99.4571   $99.46   $99.45   $99.50  
  Purchase #2 $97.84   12.820%   $110.3831   $110.38   $110.40   $110.40  
  Purchase #3 $140.98   9.676%   $154.6212   $154.62   $154.60   $154.60  
  Purchase #4 $24.54   8.845%   $26.7106   $26.71   $26.70   $26.70  
  Purchase #5 $39.53   10.534%   $43.6941   $43.69   $43.70   $43.70  
  Purchase #6 $177.99   7.280%   $190.9477   $190.95   $190.95   $190.90  
  Purchase #7 $111.53   13.181%   $126.2308   $126.23   $126.25   $126.20  
  7 purchase totals = $687.85       $752.0446   $752.04   $752.05   $752.00