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 $60.73   5.786%   $64.2438   $64.24   $64.25   $64.20  
  Purchase #2 $96.84   7.397%   $104.0033   $104.00   $104.00   $104.00  
  Purchase #3 $174.54   4.368%   $182.1639   $182.16   $182.15   $182.20  
  Purchase #4 $181.86   9.646%   $199.4022   $199.40   $199.40   $199.40  
  Purchase #5 $208.52   13.361%   $236.3804   $236.38   $236.40   $236.40  
  Purchase #6 $71.75   13.772%   $81.6314   $81.63   $81.65   $81.60  
  Purchase #7 $190.92   8.650%   $207.4346   $207.43   $207.45   $207.40  
  7 purchase totals = $985.16       $1,075.2596   $1,075.24   $1,075.30   $1,075.20