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 $61.69   9.165%   $67.3439   $67.34   $67.35   $67.30  
  Purchase #2 $170.41   4.676%   $178.3784   $178.38   $178.40   $178.40  
  Purchase #3 $250.76   7.763%   $270.2265   $270.23   $270.25   $270.20  
  Purchase #4 $70.73   8.582%   $76.8   $76.80   $76.80   $76.80  
  Purchase #5 $122.44   3.811%   $127.1062   $127.11   $127.10   $127.10  
  Purchase #6 $164.70   13.296%   $186.5985   $186.60   $186.60   $186.60  
  Purchase #7 $56.98   3.817%   $59.1549   $59.15   $59.15   $59.20  
  7 purchase totals = $897.71       $965.6084   $965.61   $965.65   $965.60