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	$158.81	12.682%	$178.9503	$178.95	$178.95	$179.00
Purchase #2	$58.99	3.546%	$61.0818	$61.08	$61.10	$61.10
Purchase #3	$36.65	10.567%	$40.5228	$40.52	$40.50	$40.50
Purchase #4	$108.38	10.194%	$119.4283	$119.43	$119.45	$119.40
Purchase #5	$101.67	3.860%	$105.5945	$105.59	$105.60	$105.60
Purchase #6	$107.94	3.500%	$111.7179	$111.72	$111.70	$111.70
Purchase #7	$20.26	8.279%	$21.9373	$21.94	$21.95	$21.90
7 purchase totals =	$592.70		$639.2329	$639.23	$639.25	$639.20