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 $23.56   10.211%   $25.9657   $25.97   $25.95   $26.00  
  Purchase #2 $232.40   12.691%   $261.8939   $261.89   $261.90   $261.90  
  Purchase #3 $69.46   11.723%   $77.6028   $77.60   $77.60   $77.60  
  Purchase #4 $112.27   9.739%   $123.204   $123.20   $123.20   $123.20  
  Purchase #5 $188.38   9.592%   $206.4494   $206.45   $206.45   $206.40  
  Purchase #6 $242.67   6.814%   $259.2055   $259.21   $259.20   $259.20  
  Purchase #7 $234.90   8.320%   $254.4437   $254.44   $254.45   $254.40  
  7 purchase totals = $1,103.64       $1,208.7650   $1,208.76   $1,208.75   $1,208.70