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 $240.94   8.645%   $261.7693   $261.77   $261.75   $261.80  
  Purchase #2 $138.78   10.737%   $153.6808   $153.68   $153.70   $153.70  
  Purchase #3 $89.46   8.334%   $96.9156   $96.92   $96.90   $96.90  
  Purchase #4 $66.44   8.382%   $72.009   $72.01   $72.00   $72.00  
  Purchase #5 $98.91   13.680%   $112.4409   $112.44   $112.45   $112.40  
  Purchase #6 $98.78   8.597%   $107.2721   $107.27   $107.25   $107.30  
  Purchase #7 $80.51   13.692%   $91.5334   $91.53   $91.55   $91.50  
  7 purchase totals = $813.82       $895.6211   $895.62   $895.60   $895.60