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	$16.34	3.444%	$16.9027	$16.90	$16.90	$16.90
Purchase #2	$102.91	13.390%	$116.6896	$116.69	$116.70	$116.70
Purchase #3	$193.83	10.590%	$214.3566	$214.36	$214.35	$214.40
Purchase #4	$34.34	11.153%	$38.1699	$38.17	$38.15	$38.20
Purchase #5	$79.89	13.552%	$90.7167	$90.72	$90.70	$90.70
Purchase #6	$99.34	8.825%	$108.1068	$108.11	$108.10	$108.10
Purchase #7	$139.82	4.759%	$146.474	$146.47	$146.45	$146.50
7 purchase totals =	$666.47		$731.4163	$731.42	$731.35	$731.50