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	$63.92	6.816%	$68.2768	$68.28	$68.30	$68.30
Purchase #2	$163.37	6.169%	$173.4483	$173.45	$173.45	$173.40
Purchase #3	$105.37	6.202%	$111.905	$111.91	$111.90	$111.90
Purchase #4	$144.93	3.103%	$149.4272	$149.43	$149.45	$149.40
Purchase #5	$85.92	4.733%	$89.9866	$89.99	$90.00	$90.00
Purchase #6	$235.99	12.145%	$264.651	$264.65	$264.65	$264.70
Purchase #7	$118.91	10.435%	$131.3183	$131.32	$131.30	$131.30
7 purchase totals =	$918.41		$989.0132	$989.03	$989.05	$989.00