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 $24.32   9.828%   $26.7102   $26.71   $26.70   $26.70  
  Purchase #2 $218.84   9.328%   $239.2534   $239.25   $239.25   $239.30  
  Purchase #3 $68.51   8.697%   $74.4683   $74.47   $74.45   $74.50  
  Purchase #4 $50.76   11.136%   $56.4126   $56.41   $56.40   $56.40  
  Purchase #5 $11.84   4.380%   $12.3586   $12.36   $12.35   $12.40  
  Purchase #6 $23.75   7.116%   $25.4401   $25.44   $25.45   $25.40  
  Purchase #7 $214.50   10.807%   $237.681   $237.68   $237.70   $237.70  
  7 purchase totals = $612.52       $672.3242   $672.32   $672.30   $672.40