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	$161.43	7.430%	$173.4242	$173.42	$173.40	$173.40
Purchase #2	$231.79	13.702%	$263.5499	$263.55	$263.55	$263.50
Purchase #3	$18.94	9.177%	$20.6781	$20.68	$20.70	$20.70
Purchase #4	$56.89	4.318%	$59.3465	$59.35	$59.35	$59.30
Purchase #5	$240.38	13.115%	$271.9058	$271.91	$271.90	$271.90
Purchase #6	$127.38	8.325%	$137.9844	$137.98	$138.00	$138.00
Purchase #7	$143.47	3.323%	$148.2375	$148.24	$148.25	$148.20
7 purchase totals =	$980.28		$1,075.1264	$1,075.13	$1,075.15	$1,075.00