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 $63.82   9.216%   $69.7017   $69.70   $69.70   $69.70  
  Purchase #2 $37.81   7.328%   $40.5807   $40.58   $40.60   $40.60  
  Purchase #3 $66.76   5.325%   $70.315   $70.32   $70.30   $70.30  
  Purchase #4 $65.80   5.246%   $69.2519   $69.25   $69.25   $69.30  
  Purchase #5 $41.36   12.703%   $46.614   $46.61   $46.60   $46.60  
  Purchase #6 $185.43   12.551%   $208.7033   $208.70   $208.70   $208.70  
  Purchase #7 $50.54   8.123%   $54.6454   $54.65   $54.65   $54.60  
  7 purchase totals = $511.52       $559.8120   $559.81   $559.80   $559.80