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	$149.93	3.664%	$155.4234	$155.42	$155.40	$155.40
Purchase #2	$173.35	13.191%	$196.2166	$196.22	$196.20	$196.20
Purchase #3	$104.43	3.444%	$108.0266	$108.03	$108.05	$108.00
Purchase #4	$104.65	12.105%	$117.3179	$117.32	$117.30	$117.30
Purchase #5	$132.52	5.201%	$139.4124	$139.41	$139.40	$139.40
Purchase #6	$89.50	11.633%	$99.9115	$99.91	$99.90	$99.90
Purchase #7	$51.50	6.284%	$54.7363	$54.74	$54.75	$54.70
7 purchase totals =	$805.88		$871.0447	$871.05	$871.00	$870.90