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 $49.36   13.120%   $55.836   $55.84   $55.85   $55.80  
  Purchase #2 $222.41   10.328%   $245.3805   $245.38   $245.40   $245.40  
  Purchase #3 $248.96   3.528%   $257.7433   $257.74   $257.75   $257.70  
  Purchase #4 $54.93   9.181%   $59.9731   $59.97   $59.95   $60.00  
  Purchase #5 $183.75   9.257%   $200.7597   $200.76   $200.75   $200.80  
  Purchase #6 $64.63   13.381%   $73.2781   $73.28   $73.30   $73.30  
  Purchase #7 $82.55   12.135%   $92.5674   $92.57   $92.55   $92.60  
  7 purchase totals = $906.59       $985.5381   $985.54   $985.55   $985.60