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	$53.62	12.209%	$60.1665	$60.17	$60.15	$60.20
Purchase #2	$83.83	13.527%	$95.1697	$95.17	$95.15	$95.20
Purchase #3	$115.52	6.605%	$123.1501	$123.15	$123.15	$123.20
Purchase #4	$35.32	7.720%	$38.0467	$38.05	$38.05	$38.00
Purchase #5	$150.47	11.696%	$168.069	$168.07	$168.05	$168.10
Purchase #6	$5.94	5.374%	$6.2592	$6.26	$6.25	$6.30
Purchase #7	$92.30	9.287%	$100.8719	$100.87	$100.85	$100.90
7 purchase totals =	$537.00		$591.7331	$591.74	$591.65	$591.90