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 $210.45   12.752%   $237.2866   $237.29   $237.30   $237.30  
  Purchase #2 $153.26   8.724%   $166.6304   $166.63   $166.65   $166.60  
  Purchase #3 $15.48   13.582%   $17.5825   $17.58   $17.60   $17.60  
  Purchase #4 $236.53   10.415%   $261.1646   $261.16   $261.15   $261.20  
  Purchase #5 $173.91   12.609%   $195.8383   $195.84   $195.85   $195.80  
  Purchase #6 $32.59   5.563%   $34.403   $34.40   $34.40   $34.40  
  Purchase #7 $130.32   8.488%   $141.3816   $141.38   $141.40   $141.40  
  7 purchase totals = $952.54       $1,054.2870   $1,054.28   $1,054.35   $1,054.30