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	$127.81	7.727%	$137.6859	$137.69	$137.70	$137.70
Purchase #2	$108.96	13.211%	$123.3547	$123.35	$123.35	$123.40
Purchase #3	$125.95	10.198%	$138.7944	$138.79	$138.80	$138.80
Purchase #4	$112.43	12.162%	$126.1037	$126.10	$126.10	$126.10
Purchase #5	$167.93	12.104%	$188.2562	$188.26	$188.25	$188.30
Purchase #6	$239.45	7.811%	$258.1534	$258.15	$258.15	$258.20
Purchase #7	$106.94	4.284%	$111.5213	$111.52	$111.50	$111.50
7 purchase totals =	$989.47		$1,083.8696	$1,083.86	$1,083.85	$1,084.00