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 $68.83   3.388%   $71.162   $71.16   $71.15   $71.20  
  Purchase #2 $165.94   6.436%   $176.6199   $176.62   $176.60   $176.60  
  Purchase #3 $45.58   3.121%   $47.0026   $47.00   $47.00   $47.00  
  Purchase #4 $237.99   10.337%   $262.591   $262.59   $262.60   $262.60  
  Purchase #5 $136.36   5.353%   $143.6594   $143.66   $143.65   $143.70  
  Purchase #6 $197.76   4.291%   $206.2459   $206.25   $206.25   $206.20  
  Purchase #7 $78.38   5.760%   $82.8947   $82.89   $82.90   $82.90  
  7 purchase totals = $930.84       $990.1755   $990.17   $990.15   $990.20