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	$95.30	9.462%	$104.3173	$104.32	$104.30	$104.30
Purchase #2	$240.91	5.812%	$254.9117	$254.91	$254.90	$254.90
Purchase #3	$102.70	10.781%	$113.7721	$113.77	$113.75	$113.80
Purchase #4	$70.60	4.739%	$73.9457	$73.95	$73.95	$73.90
Purchase #5	$103.72	7.186%	$111.1733	$111.17	$111.15	$111.20
Purchase #6	$158.50	9.162%	$173.0218	$173.02	$173.00	$173.00
Purchase #7	$114.77	10.685%	$127.0332	$127.03	$127.05	$127.00
7 purchase totals =	$886.50		$958.1751	$958.17	$958.10	$958.10