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 $215.89   13.256%   $244.5084   $244.51   $244.50   $244.50  
  Purchase #2 $134.87   8.553%   $146.4054   $146.41   $146.40   $146.40  
  Purchase #3 $53.81   13.456%   $61.0507   $61.05   $61.05   $61.10  
  Purchase #4 $14.43   12.608%   $16.2493   $16.25   $16.25   $16.20  
  Purchase #5 $167.58   5.693%   $177.1203   $177.12   $177.10   $177.10  
  Purchase #6 $128.54   6.636%   $137.0699   $137.07   $137.05   $137.10  
  Purchase #7 $168.63   12.872%   $190.3361   $190.34   $190.35   $190.30  
  7 purchase totals = $883.75       $972.7401   $972.75   $972.70   $972.70