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 $68.53   8.209%   $74.1556   $74.16   $74.15   $74.20  
  Purchase #2 $58.86   11.665%   $65.726   $65.73   $65.75   $65.70  
  Purchase #3 $49.28   7.767%   $53.1076   $53.11   $53.10   $53.10  
  Purchase #4 $115.72   5.771%   $122.3982   $122.40   $122.40   $122.40  
  Purchase #5 $151.27   11.458%   $168.6025   $168.60   $168.60   $168.60  
  Purchase #6 $221.29   9.463%   $242.2307   $242.23   $242.25   $242.20  
  Purchase #7 $240.86   8.473%   $261.2681   $261.27   $261.25   $261.30  
  7 purchase totals = $905.81       $987.4887   $987.50   $987.50   $987.50