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 $248.55   5.147%   $261.3429   $261.34   $261.35   $261.30  
  Purchase #2 $21.69   4.177%   $22.596   $22.60   $22.60   $22.60  
  Purchase #3 $172.39   10.622%   $190.7013   $190.70   $190.70   $190.70  
  Purchase #4 $186.86   4.574%   $195.407   $195.41   $195.40   $195.40  
  Purchase #5 $111.58   4.123%   $116.1804   $116.18   $116.20   $116.20  
  Purchase #6 $71.44   4.802%   $74.8705   $74.87   $74.85   $74.90  
  Purchase #7 $87.50   7.740%   $94.2725   $94.27   $94.25   $94.30  
  7 purchase totals = $900.01       $955.3706   $955.37   $955.35   $955.40