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	$31.99	6.817%	$34.1708	$34.17	$34.15	$34.20
Purchase #2	$68.82	4.305%	$71.7827	$71.78	$71.80	$71.80
Purchase #3	$20.27	10.711%	$22.4411	$22.44	$22.45	$22.40
Purchase #4	$146.42	9.841%	$160.8292	$160.83	$160.85	$160.80
Purchase #5	$77.50	6.415%	$82.4716	$82.47	$82.45	$82.50
Purchase #6	$66.78	8.514%	$72.4656	$72.47	$72.45	$72.50
Purchase #7	$120.83	13.773%	$137.4719	$137.47	$137.45	$137.50
7 purchase totals =	$532.61		$581.6329	$581.63	$581.60	$581.70