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 $119.78   6.601%   $127.6867   $127.69   $127.70   $127.70  
  Purchase #2 $182.48   9.626%   $200.0455   $200.05   $200.05   $200.00  
  Purchase #3 $12.33   11.106%   $13.6994   $13.70   $13.70   $13.70  
  Purchase #4 $53.26   8.202%   $57.6284   $57.63   $57.65   $57.60  
  Purchase #5 $250.27   7.661%   $269.4432   $269.44   $269.45   $269.40  
  Purchase #6 $119.92   5.619%   $126.6583   $126.66   $126.65   $126.70  
  Purchase #7 $77.63   11.306%   $86.4068   $86.41   $86.40   $86.40  
  7 purchase totals = $815.67       $881.5683   $881.58   $881.60   $881.50