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	$14.66	8.348%	$15.8838	$15.88	$15.90	$15.90
Purchase #2	$102.50	8.800%	$111.52	$111.52	$111.50	$111.50
Purchase #3	$91.58	5.856%	$96.9429	$96.94	$96.95	$96.90
Purchase #4	$20.46	13.136%	$23.1476	$23.15	$23.15	$23.10
Purchase #5	$214.89	10.481%	$237.4126	$237.41	$237.40	$237.40
Purchase #6	$118.78	11.536%	$132.4825	$132.48	$132.50	$132.50
Purchase #7	$97.41	9.607%	$106.7682	$106.77	$106.75	$106.80
7 purchase totals =	$660.28		$724.1576	$724.15	$724.15	$724.10