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	$27.27	9.429%	$29.8413	$29.84	$29.85	$29.80
Purchase #2	$173.31	9.698%	$190.1176	$190.12	$190.10	$190.10
Purchase #3	$7.66	10.471%	$8.4621	$8.46	$8.45	$8.50
Purchase #4	$135.96	11.105%	$151.0584	$151.06	$151.05	$151.10
Purchase #5	$127.64	4.670%	$133.6008	$133.60	$133.60	$133.60
Purchase #6	$166.43	4.224%	$173.46	$173.46	$173.45	$173.50
Purchase #7	$54.69	10.496%	$60.4303	$60.43	$60.45	$60.40
7 purchase totals =	$692.96		$746.9705	$746.97	$746.95	$747.00