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 $239.67   7.747%   $258.2372   $258.24   $258.25   $258.20  
  Purchase #2 $190.63   3.784%   $197.8434   $197.84   $197.85   $197.80  
  Purchase #3 $159.86   10.719%   $176.9954   $177.00   $177.00   $177.00  
  Purchase #4 $250.99   3.782%   $260.4824   $260.48   $260.50   $260.50  
  Purchase #5 $222.78   13.223%   $252.2382   $252.24   $252.25   $252.20  
  Purchase #6 $40.32   3.137%   $41.5848   $41.58   $41.60   $41.60  
  Purchase #7 $123.42   9.258%   $134.8462   $134.85   $134.85   $134.80  
  7 purchase totals = $1,227.67       $1,322.2276   $1,322.23   $1,322.30   $1,322.10