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	$158.47	13.571%	$179.976	$179.98	$180.00	$180.00
Purchase #2	$144.42	6.540%	$153.8651	$153.87	$153.85	$153.90
Purchase #3	$96.69	9.286%	$105.6686	$105.67	$105.65	$105.70
Purchase #4	$235.95	4.838%	$247.3653	$247.37	$247.35	$247.40
Purchase #5	$141.41	7.220%	$151.6198	$151.62	$151.60	$151.60
Purchase #6	$91.52	9.563%	$100.2721	$100.27	$100.25	$100.30
Purchase #7	$65.58	10.532%	$72.4869	$72.49	$72.50	$72.50
7 purchase totals =	$934.04		$1,011.2538	$1,011.27	$1,011.20	$1,011.40