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	$53.79	11.313%	$59.8753	$59.88	$59.90	$59.90
Purchase #2	$181.47	7.258%	$194.6411	$194.64	$194.65	$194.60
Purchase #3	$205.95	13.431%	$233.6111	$233.61	$233.60	$233.60
Purchase #4	$45.86	7.839%	$49.455	$49.46	$49.45	$49.50
Purchase #5	$166.73	3.629%	$172.7806	$172.78	$172.80	$172.80
Purchase #6	$93.68	12.195%	$105.1043	$105.10	$105.10	$105.10
Purchase #7	$42.71	13.464%	$48.4605	$48.46	$48.45	$48.50
7 purchase totals =	$790.19		$863.9279	$863.93	$863.95	$864.00