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	$165.97	4.133%	$172.8295	$172.83	$172.85	$172.80
Purchase #2	$150.45	5.261%	$158.3652	$158.37	$158.35	$158.40
Purchase #3	$72.92	6.403%	$77.5891	$77.59	$77.60	$77.60
Purchase #4	$53.78	10.160%	$59.244	$59.24	$59.25	$59.20
Purchase #5	$17.71	9.671%	$19.4227	$19.42	$19.40	$19.40
Purchase #6	$242.62	11.708%	$271.0259	$271.03	$271.05	$271.00
Purchase #7	$42.98	3.354%	$44.4215	$44.42	$44.40	$44.40
7 purchase totals =	$746.43		$802.8979	$802.90	$802.90	$802.80