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 $94.81   3.715%   $98.3322   $98.33   $98.35   $98.30  
  Purchase #2 $159.44   5.700%   $168.5281   $168.53   $168.55   $168.50  
  Purchase #3 $34.91   4.537%   $36.4939   $36.49   $36.50   $36.50  
  Purchase #4 $243.28   7.644%   $261.8763   $261.88   $261.90   $261.90  
  Purchase #5 $140.38   9.246%   $153.3595   $153.36   $153.35   $153.40  
  Purchase #6 $138.30   12.422%   $155.4796   $155.48   $155.50   $155.50  
  Purchase #7 $85.72   11.315%   $95.4192   $95.42   $95.40   $95.40  
  7 purchase totals = $896.84       $969.4888   $969.49   $969.55   $969.50