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 $103.87   11.577%   $115.895   $115.90   $115.90   $115.90  
  Purchase #2 $109.33   12.499%   $122.9952   $123.00   $123.00   $123.00  
  Purchase #3 $71.90   9.218%   $78.5277   $78.53   $78.55   $78.50  
  Purchase #4 $171.76   8.734%   $186.7615   $186.76   $186.75   $186.80  
  Purchase #5 $135.40   12.212%   $151.935   $151.94   $151.95   $151.90  
  Purchase #6 $248.27   4.690%   $259.9139   $259.91   $259.90   $259.90  
  Purchase #7 $234.86   11.155%   $261.0586   $261.06   $261.05   $261.10  
  7 purchase totals = $1,075.39       $1,177.0869   $1,177.10   $1,177.10   $1,177.10