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 $69.40   10.466%   $76.6634   $76.66   $76.65   $76.70  
  Purchase #2 $34.38   8.849%   $37.4223   $37.42   $37.40   $37.40  
  Purchase #3 $79.54   3.758%   $82.5291   $82.53   $82.55   $82.50  
  Purchase #4 $60.71   8.484%   $65.8606   $65.86   $65.85   $65.90  
  Purchase #5 $214.86   10.317%   $237.0271   $237.03   $237.05   $237.00  
  Purchase #6 $242.76   11.538%   $270.7696   $270.77   $270.75   $270.80  
  Purchase #7 $8.89   6.298%   $9.4499   $9.45   $9.45   $9.40  
  7 purchase totals = $710.54       $779.7220   $779.72   $779.70   $779.70