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 $228.90   5.552%   $241.6085   $241.61   $241.60   $241.60  
  Purchase #2 $45.46   7.787%   $49   $49.00   $49.00   $49.00  
  Purchase #3 $22.48   10.117%   $24.7543   $24.75   $24.75   $24.80  
  Purchase #4 $74.87   4.765%   $78.4376   $78.44   $78.45   $78.40  
  Purchase #5 $70.87   8.339%   $76.7798   $76.78   $76.80   $76.80  
  Purchase #6 $15.48   13.130%   $17.5125   $17.51   $17.50   $17.50  
  Purchase #7 $217.41   3.422%   $224.8498   $224.85   $224.85   $224.80  
  7 purchase totals = $675.47       $712.9425   $712.94   $712.95   $712.90