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 $188.43   6.118%   $199.9581   $199.96   $199.95   $200.00  
  Purchase #2 $172.92   13.134%   $195.6313   $195.63   $195.65   $195.60  
  Purchase #3 $89.50   7.690%   $96.3826   $96.38   $96.40   $96.40  
  Purchase #4 $116.28   7.154%   $124.5987   $124.60   $124.60   $124.60  
  Purchase #5 $248.81   6.785%   $265.6918   $265.69   $265.70   $265.70  
  Purchase #6 $43.52   8.614%   $47.2688   $47.27   $47.25   $47.30  
  Purchase #7 $37.99   12.418%   $42.7076   $42.71   $42.70   $42.70  
  7 purchase totals = $897.45       $972.2389   $972.24   $972.25   $972.30