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 $209.49   13.372%   $237.503   $237.50   $237.50   $237.50  
  Purchase #2 $114.99   3.327%   $118.8157   $118.82   $118.80   $118.80  
  Purchase #3 $213.48   11.794%   $238.6578   $238.66   $238.65   $238.70  
  Purchase #4 $76.86   5.503%   $81.0896   $81.09   $81.10   $81.10  
  Purchase #5 $248.77   6.103%   $263.9524   $263.95   $263.95   $264.00  
  Purchase #6 $49.68   12.374%   $55.8274   $55.83   $55.85   $55.80  
  Purchase #7 $23.42   8.612%   $25.4369   $25.44   $25.45   $25.40  
  7 purchase totals = $936.69       $1,021.2828   $1,021.29   $1,021.30   $1,021.30