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 $60.46   5.149%   $63.5731   $63.57   $63.55   $63.60  
  Purchase #2 $36.50   5.463%   $38.494   $38.49   $38.50   $38.50  
  Purchase #3 $182.81   9.381%   $199.9594   $199.96   $199.95   $200.00  
  Purchase #4 $214.25   8.491%   $232.442   $232.44   $232.45   $232.40  
  Purchase #5 $152.89   6.829%   $163.3309   $163.33   $163.35   $163.30  
  Purchase #6 $30.76   10.806%   $34.0839   $34.08   $34.10   $34.10  
  Purchase #7 $85.71   4.432%   $89.5087   $89.51   $89.50   $89.50  
  7 purchase totals = $763.38       $821.3920   $821.38   $821.40   $821.40