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 $213.42   6.719%   $227.7597   $227.76   $227.75   $227.80  
  Purchase #2 $20.27   11.713%   $22.6442   $22.64   $22.65   $22.60  
  Purchase #3 $123.42   5.105%   $129.7206   $129.72   $129.70   $129.70  
  Purchase #4 $55.33   4.312%   $57.7158   $57.72   $57.70   $57.70  
  Purchase #5 $78.35   3.247%   $80.894   $80.89   $80.90   $80.90  
  Purchase #6 $81.81   11.674%   $91.3605   $91.36   $91.35   $91.40  
  Purchase #7 $105.56   8.381%   $114.407   $114.41   $114.40   $114.40  
  7 purchase totals = $678.16       $724.5018   $724.50   $724.45   $724.50