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	$33.45	3.623%	$34.6619	$34.66	$34.65	$34.70
Purchase #2	$105.83	5.379%	$111.5226	$111.52	$111.50	$111.50
Purchase #3	$137.92	8.484%	$149.6211	$149.62	$149.60	$149.60
Purchase #4	$146.98	13.839%	$167.3206	$167.32	$167.30	$167.30
Purchase #5	$115.89	10.156%	$127.6598	$127.66	$127.65	$127.70
Purchase #6	$135.42	4.851%	$141.9892	$141.99	$142.00	$142.00
Purchase #7	$117.72	8.838%	$128.1241	$128.12	$128.10	$128.10
7 purchase totals =	$793.21		$860.8993	$860.89	$860.80	$860.90