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 $69.95   11.734%   $78.1579   $78.16   $78.15   $78.20  
  Purchase #2 $129.63   6.271%   $137.7591   $137.76   $137.75   $137.80  
  Purchase #3 $67.90   4.413%   $70.8964   $70.90   $70.90   $70.90  
  Purchase #4 $208.88   6.428%   $222.3068   $222.31   $222.30   $222.30  
  Purchase #5 $219.77   13.116%   $248.595   $248.60   $248.60   $248.60  
  Purchase #6 $148.51   10.169%   $163.612   $163.61   $163.60   $163.60  
  Purchase #7 $78.93   7.636%   $84.9571   $84.96   $84.95   $85.00  
  7 purchase totals = $923.57       $1,006.2843   $1,006.30   $1,006.25   $1,006.40