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 $114.82   10.567%   $126.953   $126.95   $126.95   $127.00  
  Purchase #2 $109.87   7.117%   $117.6894   $117.69   $117.70   $117.70  
  Purchase #3 $39.46   5.159%   $41.4957   $41.50   $41.50   $41.50  
  Purchase #4 $126.87   13.423%   $143.8998   $143.90   $143.90   $143.90  
  Purchase #5 $74.44   3.818%   $77.2821   $77.28   $77.30   $77.30  
  Purchase #6 $62.51   11.677%   $69.8093   $69.81   $69.80   $69.80  
  Purchase #7 $249.25   5.422%   $262.7643   $262.76   $262.75   $262.80  
  7 purchase totals = $777.22       $839.8936   $839.89   $839.90   $840.00