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 $55.56   12.703%   $62.6178   $62.62   $62.60   $62.60  
  Purchase #2 $13.53   11.237%   $15.0504   $15.05   $15.05   $15.10  
  Purchase #3 $241.64   9.135%   $263.7138   $263.71   $263.70   $263.70  
  Purchase #4 $59.28   6.189%   $62.9488   $62.95   $62.95   $62.90  
  Purchase #5 $34.44   6.772%   $36.7723   $36.77   $36.75   $36.80  
  Purchase #6 $231.44   12.403%   $260.1455   $260.15   $260.15   $260.10  
  Purchase #7 $112.67   8.728%   $122.5038   $122.50   $122.50   $122.50  
  7 purchase totals = $748.56       $823.7524   $823.75   $823.70   $823.70