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	$242.83	10.516%	$268.366	$268.37	$268.35	$268.40
Purchase #2	$146.59	6.743%	$156.4746	$156.47	$156.45	$156.50
Purchase #3	$229.74	3.188%	$237.0641	$237.06	$237.05	$237.10
Purchase #4	$105.78	11.766%	$118.2261	$118.23	$118.25	$118.20
Purchase #5	$42.65	5.561%	$45.0218	$45.02	$45.00	$45.00
Purchase #6	$39.86	8.209%	$43.1321	$43.13	$43.15	$43.10
Purchase #7	$107.97	3.362%	$111.6	$111.60	$111.60	$111.60
7 purchase totals =	$915.42		$979.8847	$979.88	$979.85	$979.90