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	$26.68	8.196%	$28.8667	$28.87	$28.85	$28.90
Purchase #2	$111.55	4.689%	$116.7806	$116.78	$116.80	$116.80
Purchase #3	$135.97	6.123%	$144.2954	$144.30	$144.30	$144.30
Purchase #4	$76.47	12.824%	$86.2765	$86.28	$86.30	$86.30
Purchase #5	$144.40	4.677%	$151.1536	$151.15	$151.15	$151.20
Purchase #6	$158.59	13.344%	$179.7522	$179.75	$179.75	$179.80
Purchase #7	$96.42	3.125%	$99.4331	$99.43	$99.45	$99.40
7 purchase totals =	$750.08		$806.5581	$806.56	$806.60	$806.70