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 $239.63   12.504%   $269.5933   $269.59   $269.60   $269.60  
  Purchase #2 $110.30   8.240%   $119.3887   $119.39   $119.40   $119.40  
  Purchase #3 $145.65   13.126%   $164.768   $164.77   $164.75   $164.80  
  Purchase #4 $202.93   11.630%   $226.5308   $226.53   $226.55   $226.50  
  Purchase #5 $176.92   9.868%   $194.3785   $194.38   $194.40   $194.40  
  Purchase #6 $62.27   3.822%   $64.65   $64.65   $64.65   $64.70  
  Purchase #7 $127.36   10.408%   $140.6156   $140.62   $140.60   $140.60  
  7 purchase totals = $1,065.06       $1,179.9249   $1,179.93   $1,179.95   $1,180.00