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	$138.85	10.538%	$153.482	$153.48	$153.50	$153.50
Purchase #2	$118.89	8.194%	$128.6318	$128.63	$128.65	$128.60
Purchase #3	$247.34	3.383%	$255.7075	$255.71	$255.70	$255.70
Purchase #4	$11.77	6.670%	$12.5551	$12.56	$12.55	$12.60
Purchase #5	$105.36	5.356%	$111.0031	$111.00	$111.00	$111.00
Purchase #6	$52.91	9.365%	$57.865	$57.87	$57.85	$57.90
Purchase #7	$72.59	6.114%	$77.0282	$77.03	$77.05	$77.00
7 purchase totals =	$747.71		$796.2727	$796.28	$796.30	$796.30