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	$59.42	11.321%	$66.1469	$66.15	$66.15	$66.10
Purchase #2	$48.75	9.262%	$53.2652	$53.27	$53.25	$53.30
Purchase #3	$136.57	10.820%	$151.3469	$151.35	$151.35	$151.30
Purchase #4	$34.34	12.222%	$38.537	$38.54	$38.55	$38.50
Purchase #5	$47.66	11.468%	$53.1256	$53.13	$53.15	$53.10
Purchase #6	$11.58	7.608%	$12.461	$12.46	$12.45	$12.50
Purchase #7	$249.71	12.241%	$280.277	$280.28	$280.30	$280.30
7 purchase totals =	$588.03		$655.1596	$655.18	$655.20	$655.10