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	$243.61	13.129%	$275.5936	$275.59	$275.60	$275.60
Purchase #2	$249.88	13.144%	$282.7242	$282.72	$282.70	$282.70
Purchase #3	$160.83	11.256%	$178.933	$178.93	$178.95	$178.90
Purchase #4	$90.49	11.145%	$100.5751	$100.58	$100.60	$100.60
Purchase #5	$92.28	12.158%	$103.4994	$103.50	$103.50	$103.50
Purchase #6	$244.64	10.866%	$271.2226	$271.22	$271.20	$271.20
Purchase #7	$183.39	5.488%	$193.4544	$193.45	$193.45	$193.50
7 purchase totals =	$1,265.12		$1,406.0023	$1,405.99	$1,406.00	$1,406.00