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 $236.99   3.592%   $245.5027   $245.50   $245.50   $245.50  
  Purchase #2 $45.94   10.543%   $50.7835   $50.78   $50.80   $50.80  
  Purchase #3 $55.38   5.638%   $58.5023   $58.50   $58.50   $58.50  
  Purchase #4 $117.76   6.417%   $125.3167   $125.32   $125.30   $125.30  
  Purchase #5 $114.71   3.141%   $118.313   $118.31   $118.30   $118.30  
  Purchase #6 $21.33   9.216%   $23.2958   $23.30   $23.30   $23.30  
  Purchase #7 $124.94   6.680%   $133.286   $133.29   $133.30   $133.30  
  7 purchase totals = $717.05       $755.0000   $755.00   $755.00   $755.00