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 $226.89   10.606%   $250.954   $250.95   $250.95   $251.00  
  Purchase #2 $29.40   3.269%   $30.3611   $30.36   $30.35   $30.40  
  Purchase #3 $246.88   3.860%   $256.4096   $256.41   $256.40   $256.40  
  Purchase #4 $213.65   11.671%   $238.5851   $238.59   $238.60   $238.60  
  Purchase #5 $107.87   5.813%   $114.1405   $114.14   $114.15   $114.10  
  Purchase #6 $203.33   4.729%   $212.9455   $212.95   $212.95   $212.90  
  Purchase #7 $248.29   5.518%   $261.9906   $261.99   $262.00   $262.00  
  7 purchase totals = $1,276.31       $1,365.3864   $1,365.39   $1,365.40   $1,365.40