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 $63.94   10.271%   $70.5073   $70.51   $70.50   $70.50  
  Purchase #2 $127.27   7.568%   $136.9018   $136.90   $136.90   $136.90  
  Purchase #3 $58.98   10.382%   $65.1033   $65.10   $65.10   $65.10  
  Purchase #4 $230.61   11.432%   $256.9733   $256.97   $256.95   $257.00  
  Purchase #5 $154.31   9.344%   $168.7287   $168.73   $168.75   $168.70  
  Purchase #6 $116.43   5.505%   $122.8395   $122.84   $122.85   $122.80  
  Purchase #7 $140.63   7.613%   $151.3362   $151.34   $151.35   $151.30  
  7 purchase totals = $892.17       $972.3901   $972.39   $972.40   $972.30