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 $25.76   3.216%   $26.5884   $26.59   $26.60   $26.60  
  Purchase #2 $132.47   5.718%   $140.0446   $140.04   $140.05   $140.00  
  Purchase #3 $99.35   4.452%   $103.7731   $103.77   $103.75   $103.80  
  Purchase #4 $76.34   10.371%   $84.2572   $84.26   $84.25   $84.30  
  Purchase #5 $222.83   6.124%   $236.4761   $236.48   $236.50   $236.50  
  Purchase #6 $103.49   10.646%   $114.5075   $114.51   $114.50   $114.50  
  Purchase #7 $13.65   4.581%   $14.2753   $14.28   $14.30   $14.30  
  7 purchase totals = $673.89       $719.9222   $719.93   $719.95   $720.00