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 $60.66   9.534%   $66.4433   $66.44   $66.45   $66.40  
  Purchase #2 $41.75   5.516%   $44.0529   $44.05   $44.05   $44.10  
  Purchase #3 $119.98   11.675%   $133.9877   $133.99   $134.00   $134.00  
  Purchase #4 $180.66   5.427%   $190.4644   $190.46   $190.45   $190.50  
  Purchase #5 $32.63   9.273%   $35.6558   $35.66   $35.65   $35.70  
  Purchase #6 $195.72   10.685%   $216.6327   $216.63   $216.65   $216.60  
  Purchase #7 $8.96   7.681%   $9.6482   $9.65   $9.65   $9.60  
  7 purchase totals = $640.36       $696.8850   $696.88   $696.90   $696.90