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	$149.47	13.254%	$169.2808	$169.28	$169.30	$169.30
Purchase #2	$91.27	8.540%	$99.0645	$99.06	$99.05	$99.10
Purchase #3	$48.87	8.161%	$52.8583	$52.86	$52.85	$52.90
Purchase #4	$52.94	4.735%	$55.4467	$55.45	$55.45	$55.40
Purchase #5	$62.45	6.793%	$66.6922	$66.69	$66.70	$66.70
Purchase #6	$138.78	5.209%	$146.0091	$146.01	$146.00	$146.00
Purchase #7	$212.30	8.375%	$230.0801	$230.08	$230.10	$230.10
7 purchase totals =	$756.08		$819.4317	$819.43	$819.45	$819.50