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 $90.63   3.741%   $94.0205   $94.02   $94.00   $94.00  
  Purchase #2 $246.58   10.736%   $273.0528   $273.05   $273.05   $273.10  
  Purchase #3 $173.41   5.211%   $182.4464   $182.45   $182.45   $182.40  
  Purchase #4 $246.98   7.720%   $266.0469   $266.05   $266.05   $266.00  
  Purchase #5 $119.38   10.369%   $131.7585   $131.76   $131.75   $131.80  
  Purchase #6 $87.66   12.319%   $98.4588   $98.46   $98.45   $98.50  
  Purchase #7 $235.79   10.779%   $261.2058   $261.21   $261.20   $261.20  
  7 purchase totals = $1,200.43       $1,306.9897   $1,307.00   $1,306.95   $1,307.00