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	$150.85	9.816%	$165.6574	$165.66	$165.65	$165.70
Purchase #2	$83.57	10.634%	$92.4568	$92.46	$92.45	$92.50
Purchase #3	$49.26	11.235%	$54.7944	$54.79	$54.80	$54.80
Purchase #4	$19.54	8.853%	$21.2699	$21.27	$21.25	$21.30
Purchase #5	$127.47	13.402%	$144.5535	$144.55	$144.55	$144.60
Purchase #6	$231.52	4.626%	$242.2301	$242.23	$242.25	$242.20
Purchase #7	$115.62	3.852%	$120.0737	$120.07	$120.05	$120.10
7 purchase totals =	$777.83		$841.0358	$841.03	$841.00	$841.20