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	$92.67	4.218%	$96.5788	$96.58	$96.60	$96.60
Purchase #2	$93.56	8.413%	$101.4312	$101.43	$101.45	$101.40
Purchase #3	$33.52	12.171%	$37.5997	$37.60	$37.60	$37.60
Purchase #4	$99.44	4.352%	$103.7676	$103.77	$103.75	$103.80
Purchase #5	$163.38	13.583%	$185.5719	$185.57	$185.55	$185.60
Purchase #6	$48.35	10.239%	$53.3006	$53.30	$53.30	$53.30
Purchase #7	$64.60	3.218%	$66.6788	$66.68	$66.70	$66.70
7 purchase totals =	$595.52		$644.9286	$644.93	$644.95	$645.00