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 $59.26   10.814%   $65.6684   $65.67   $65.65   $65.70  
  Purchase #2 $186.89   11.685%   $208.7281   $208.73   $208.75   $208.70  
  Purchase #3 $21.76   8.459%   $23.6007   $23.60   $23.60   $23.60  
  Purchase #4 $42.43   10.723%   $46.9798   $46.98   $47.00   $47.00  
  Purchase #5 $85.25   4.643%   $89.2082   $89.21   $89.20   $89.20  
  Purchase #6 $51.87   11.262%   $57.7116   $57.71   $57.70   $57.70  
  Purchase #7 $29.42   10.120%   $32.3973   $32.40   $32.40   $32.40  
  7 purchase totals = $476.88       $524.2941   $524.30   $524.30   $524.30