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	$37.83	4.658%	$39.5921	$39.59	$39.60	$39.60
Purchase #2	$21.28	13.370%	$24.1251	$24.13	$24.15	$24.10
Purchase #3	$32.42	3.109%	$33.4279	$33.43	$33.45	$33.40
Purchase #4	$192.91	7.849%	$208.0515	$208.05	$208.05	$208.10
Purchase #5	$29.32	12.284%	$32.9217	$32.92	$32.90	$32.90
Purchase #6	$11.56	7.114%	$12.3824	$12.38	$12.40	$12.40
Purchase #7	$191.69	13.284%	$217.1541	$217.15	$217.15	$217.20
7 purchase totals =	$517.01		$567.6548	$567.65	$567.70	$567.70