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 $63.65   7.794%   $68.6109   $68.61   $68.60   $68.60  
  Purchase #2 $61.77   3.222%   $63.7602   $63.76   $63.75   $63.80  
  Purchase #3 $103.54   10.632%   $114.5484   $114.55   $114.55   $114.50  
  Purchase #4 $127.99   5.136%   $134.5636   $134.56   $134.55   $134.60  
  Purchase #5 $157.89   11.745%   $176.4342   $176.43   $176.45   $176.40  
  Purchase #6 $28.39   7.556%   $30.5351   $30.54   $30.55   $30.50  
  Purchase #7 $85.88   11.323%   $95.6042   $95.60   $95.60   $95.60  
  7 purchase totals = $629.11       $684.0566   $684.05   $684.05   $684.00