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 $216.53   13.865%   $246.5519   $246.55   $246.55   $246.60  
  Purchase #2 $191.81   13.628%   $217.9499   $217.95   $217.95   $217.90  
  Purchase #3 $107.62   9.149%   $117.4662   $117.47   $117.45   $117.50  
  Purchase #4 $180.27   10.545%   $199.2795   $199.28   $199.30   $199.30  
  Purchase #5 $21.63   7.159%   $23.1785   $23.18   $23.20   $23.20  
  Purchase #6 $241.63   13.174%   $273.4623   $273.46   $273.45   $273.50  
  Purchase #7 $60.61   9.154%   $66.1582   $66.16   $66.15   $66.20  
  7 purchase totals = $1,020.10       $1,144.0465   $1,144.05   $1,144.05   $1,144.20