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	$10.81	11.389%	$12.0412	$12.04	$12.05	$12.00
Purchase #2	$127.54	10.718%	$141.2097	$141.21	$141.20	$141.20
Purchase #3	$86.42	13.105%	$97.7453	$97.75	$97.75	$97.70
Purchase #4	$99.57	5.574%	$105.12	$105.12	$105.10	$105.10
Purchase #5	$241.97	10.268%	$266.8155	$266.82	$266.80	$266.80
Purchase #6	$225.80	3.426%	$233.5359	$233.54	$233.55	$233.50
Purchase #7	$180.92	13.310%	$205.0005	$205.00	$205.00	$205.00
7 purchase totals =	$973.03		$1,061.4681	$1,061.48	$1,061.45	$1,061.30