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	$10.62	3.586%	$11.0008	$11.00	$11.00	$11.00
Purchase #2	$98.94	5.237%	$104.1215	$104.12	$104.10	$104.10
Purchase #3	$54.92	8.724%	$59.7112	$59.71	$59.70	$59.70
Purchase #4	$89.42	11.853%	$100.019	$100.02	$100.00	$100.00
Purchase #5	$165.40	4.366%	$172.6214	$172.62	$172.60	$172.60
Purchase #6	$75.67	9.487%	$82.8488	$82.85	$82.85	$82.80
Purchase #7	$136.32	9.633%	$149.4517	$149.45	$149.45	$149.50
7 purchase totals =	$631.29		$679.7744	$679.77	$679.70	$679.70