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	$200.52	11.281%	$223.1407	$223.14	$223.15	$223.10
Purchase #2	$151.31	3.558%	$156.6936	$156.69	$156.70	$156.70
Purchase #3	$79.68	13.726%	$90.6169	$90.62	$90.60	$90.60
Purchase #4	$92.82	10.713%	$102.7638	$102.76	$102.75	$102.80
Purchase #5	$9.25	8.323%	$10.0199	$10.02	$10.00	$10.00
Purchase #6	$73.92	3.176%	$76.2677	$76.27	$76.25	$76.30
Purchase #7	$9.47	12.548%	$10.6583	$10.66	$10.65	$10.70
7 purchase totals =	$616.97		$670.1609	$670.16	$670.10	$670.20