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	$13.75	10.172%	$15.1487	$15.15	$15.15	$15.10
Purchase #2	$236.83	9.653%	$259.6912	$259.69	$259.70	$259.70
Purchase #3	$6.85	13.103%	$7.7476	$7.75	$7.75	$7.70
Purchase #4	$231.68	10.208%	$255.3299	$255.33	$255.35	$255.30
Purchase #5	$224.27	6.192%	$238.1568	$238.16	$238.15	$238.20
Purchase #6	$176.54	7.318%	$189.4592	$189.46	$189.45	$189.50
Purchase #7	$17.66	4.784%	$18.5049	$18.50	$18.50	$18.50
7 purchase totals =	$907.58		$984.0383	$984.04	$984.05	$984.00