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	$25.71	6.766%	$27.4495	$27.45	$27.45	$27.40
Purchase #2	$52.49	3.422%	$54.2862	$54.29	$54.30	$54.30
Purchase #3	$100.33	13.114%	$113.4873	$113.49	$113.50	$113.50
Purchase #4	$241.31	9.142%	$263.3706	$263.37	$263.35	$263.40
Purchase #5	$191.91	10.324%	$211.7228	$211.72	$211.70	$211.70
Purchase #6	$17.80	11.613%	$19.8671	$19.87	$19.85	$19.90
Purchase #7	$143.98	10.141%	$158.581	$158.58	$158.60	$158.60
7 purchase totals =	$773.53		$848.7645	$848.77	$848.75	$848.80