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	$145.91	6.178%	$154.9243	$154.92	$154.90	$154.90
Purchase #2	$247.43	10.204%	$272.6778	$272.68	$272.70	$272.70
Purchase #3	$53.39	10.537%	$59.0157	$59.02	$59.00	$59.00
Purchase #4	$79.66	9.699%	$87.3862	$87.39	$87.40	$87.40
Purchase #5	$53.68	10.702%	$59.4248	$59.42	$59.40	$59.40
Purchase #6	$225.52	4.264%	$235.1362	$235.14	$235.15	$235.10
Purchase #7	$42.58	7.390%	$45.7267	$45.73	$45.75	$45.70
7 purchase totals =	$848.17		$914.2917	$914.30	$914.30	$914.20