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 $240.91   8.724%   $261.927   $261.93   $261.95   $261.90  
  Purchase #2 $107.66   9.757%   $118.1644   $118.16   $118.15   $118.20  
  Purchase #3 $133.51   6.813%   $142.606   $142.61   $142.60   $142.60  
  Purchase #4 $104.26   8.513%   $113.1357   $113.14   $113.15   $113.10  
  Purchase #5 $161.69   7.333%   $173.5467   $173.55   $173.55   $173.50  
  Purchase #6 $116.28   3.406%   $120.2405   $120.24   $120.25   $120.20  
  Purchase #7 $25.98   5.458%   $27.398   $27.40   $27.40   $27.40  
  7 purchase totals = $890.29       $957.0183   $957.03   $957.05   $956.90