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	$15.90	11.754%	$17.7689	$17.77	$17.75	$17.80
Purchase #2	$91.43	11.605%	$102.0405	$102.04	$102.05	$102.00
Purchase #3	$118.92	7.347%	$127.6571	$127.66	$127.65	$127.70
Purchase #4	$78.32	5.813%	$82.8727	$82.87	$82.85	$82.90
Purchase #5	$38.49	3.451%	$39.8183	$39.82	$39.80	$39.80
Purchase #6	$10.70	4.399%	$11.1707	$11.17	$11.15	$11.20
Purchase #7	$113.82	12.705%	$128.2808	$128.28	$128.30	$128.30
7 purchase totals =	$467.58		$509.6090	$509.61	$509.55	$509.70