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 $244.65   8.826%   $266.2428   $266.24   $266.25   $266.20  
  Purchase #2 $63.36   13.624%   $71.9922   $71.99   $72.00   $72.00  
  Purchase #3 $33.58   13.346%   $38.0616   $38.06   $38.05   $38.10  
  Purchase #4 $121.35   3.248%   $125.2914   $125.29   $125.30   $125.30  
  Purchase #5 $211.78   12.859%   $239.0128   $239.01   $239.00   $239.00  
  Purchase #6 $128.71   8.537%   $139.698   $139.70   $139.70   $139.70  
  Purchase #7 $71.48   10.422%   $78.9296   $78.93   $78.95   $78.90  
  7 purchase totals = $874.91       $959.2284   $959.22   $959.25   $959.20