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	$11.70	10.356%	$12.9117	$12.91	$12.90	$12.90
Purchase #2	$159.74	8.390%	$173.1422	$173.14	$173.15	$173.10
Purchase #3	$79.47	11.262%	$88.4199	$88.42	$88.40	$88.40
Purchase #4	$83.45	8.756%	$90.7569	$90.76	$90.75	$90.80
Purchase #5	$64.37	12.504%	$72.4188	$72.42	$72.40	$72.40
Purchase #6	$247.49	9.737%	$271.5881	$271.59	$271.60	$271.60
Purchase #7	$96.57	7.830%	$104.1314	$104.13	$104.15	$104.10
7 purchase totals =	$742.79		$813.3690	$813.37	$813.35	$813.30