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	$82.46	8.639%	$89.5837	$89.58	$89.60	$89.60
Purchase #2	$186.50	9.766%	$204.7136	$204.71	$204.70	$204.70
Purchase #3	$50.86	6.725%	$54.2803	$54.28	$54.30	$54.30
Purchase #4	$138.31	5.729%	$146.2338	$146.23	$146.25	$146.20
Purchase #5	$75.93	3.299%	$78.4349	$78.43	$78.45	$78.40
Purchase #6	$130.99	10.435%	$144.6588	$144.66	$144.65	$144.70
Purchase #7	$56.65	13.247%	$64.1544	$64.15	$64.15	$64.20
7 purchase totals =	$721.70		$782.0595	$782.04	$782.10	$782.10