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	$150.91	5.255%	$158.8403	$158.84	$158.85	$158.80
Purchase #2	$69.66	10.768%	$77.161	$77.16	$77.15	$77.20
Purchase #3	$143.87	6.463%	$153.1683	$153.17	$153.15	$153.20
Purchase #4	$19.66	3.562%	$20.3603	$20.36	$20.35	$20.40
Purchase #5	$96.41	4.267%	$100.5238	$100.52	$100.50	$100.50
Purchase #6	$105.79	8.181%	$114.4447	$114.44	$114.45	$114.40
Purchase #7	$40.87	3.309%	$42.2224	$42.22	$42.20	$42.20
7 purchase totals =	$627.17		$666.7208	$666.71	$666.65	$666.70