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	$51.92	8.407%	$56.2849	$56.28	$56.30	$56.30
Purchase #2	$74.31	5.135%	$78.1258	$78.13	$78.15	$78.10
Purchase #3	$208.62	6.864%	$222.9397	$222.94	$222.95	$222.90
Purchase #4	$223.60	10.248%	$246.5145	$246.51	$246.50	$246.50
Purchase #5	$99.42	12.142%	$111.4916	$111.49	$111.50	$111.50
Purchase #6	$68.29	3.108%	$70.4125	$70.41	$70.40	$70.40
Purchase #7	$14.93	13.694%	$16.9745	$16.97	$16.95	$17.00
7 purchase totals =	$741.09		$802.7435	$802.73	$802.75	$802.70