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	$230.49	7.637%	$248.0925	$248.09	$248.10	$248.10
Purchase #2	$75.62	4.182%	$78.7824	$78.78	$78.80	$78.80
Purchase #3	$69.71	4.622%	$72.932	$72.93	$72.95	$72.90
Purchase #4	$48.93	12.570%	$55.0805	$55.08	$55.10	$55.10
Purchase #5	$72.98	7.206%	$78.2389	$78.24	$78.25	$78.20
Purchase #6	$20.87	10.269%	$23.0131	$23.01	$23.00	$23.00
Purchase #7	$78.32	4.538%	$81.8742	$81.87	$81.85	$81.90
7 purchase totals =	$596.92		$638.0136	$638.00	$638.05	$638.00