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 $183.72   5.154%   $193.1889   $193.19   $193.20   $193.20  
  Purchase #2 $125.61   11.134%   $139.5954   $139.60   $139.60   $139.60  
  Purchase #3 $217.26   12.584%   $244.6   $244.60   $244.60   $244.60  
  Purchase #4 $106.49   6.359%   $113.2617   $113.26   $113.25   $113.30  
  Purchase #5 $162.38   10.643%   $179.6621   $179.66   $179.65   $179.70  
  Purchase #6 $45.68   10.811%   $50.6185   $50.62   $50.60   $50.60  
  Purchase #7 $48.77   3.551%   $50.5018   $50.50   $50.50   $50.50  
  7 purchase totals = $889.91       $971.4284   $971.43   $971.40   $971.50