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	$21.66	11.405%	$24.1303	$24.13	$24.15	$24.10
Purchase #2	$89.79	10.573%	$99.2835	$99.28	$99.30	$99.30
Purchase #3	$62.42	6.423%	$66.4292	$66.43	$66.45	$66.40
Purchase #4	$161.70	7.262%	$173.4427	$173.44	$173.45	$173.40
Purchase #5	$157.45	6.208%	$167.2245	$167.22	$167.20	$167.20
Purchase #6	$10.83	4.553%	$11.3231	$11.32	$11.30	$11.30
Purchase #7	$63.42	11.123%	$70.4742	$70.47	$70.45	$70.50
7 purchase totals =	$567.27		$612.3075	$612.29	$612.30	$612.20