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	$53.90	12.842%	$60.8218	$60.82	$60.80	$60.80
Purchase #2	$45.85	5.390%	$48.3213	$48.32	$48.30	$48.30
Purchase #3	$100.32	10.694%	$111.0482	$111.05	$111.05	$111.00
Purchase #4	$214.69	5.558%	$226.6225	$226.62	$226.60	$226.60
Purchase #5	$172.76	13.690%	$196.4108	$196.41	$196.40	$196.40
Purchase #6	$241.73	8.149%	$261.4286	$261.43	$261.45	$261.40
Purchase #7	$242.95	10.206%	$267.7455	$267.75	$267.75	$267.70
7 purchase totals =	$1,072.20		$1,172.3987	$1,172.40	$1,172.35	$1,172.20