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	$132.31	10.566%	$146.2899	$146.29	$146.30	$146.30
Purchase #2	$29.92	4.842%	$31.3687	$31.37	$31.35	$31.40
Purchase #3	$12.65	4.528%	$13.2228	$13.22	$13.20	$13.20
Purchase #4	$144.53	9.674%	$158.5118	$158.51	$158.50	$158.50
Purchase #5	$137.28	12.272%	$154.127	$154.13	$154.15	$154.10
Purchase #6	$69.98	6.621%	$74.6134	$74.61	$74.60	$74.60
Purchase #7	$139.69	9.186%	$152.5219	$152.52	$152.50	$152.50
7 purchase totals =	$666.36		$730.6555	$730.65	$730.60	$730.60