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	$99.54	11.546%	$111.0329	$111.03	$111.05	$111.00
Purchase #2	$184.46	5.390%	$194.4024	$194.40	$194.40	$194.40
Purchase #3	$125.27	11.170%	$139.2627	$139.26	$139.25	$139.30
Purchase #4	$46.43	4.318%	$48.4348	$48.43	$48.45	$48.40
Purchase #5	$46.90	13.161%	$53.0725	$53.07	$53.05	$53.10
Purchase #6	$220.52	4.639%	$230.7499	$230.75	$230.75	$230.70
Purchase #7	$19.86	3.628%	$20.5805	$20.58	$20.60	$20.60
7 purchase totals =	$742.98		$797.5357	$797.52	$797.55	$797.50