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	$28.61	6.429%	$30.4493	$30.45	$30.45	$30.40
Purchase #2	$52.85	3.124%	$54.501	$54.50	$54.50	$54.50
Purchase #3	$239.57	12.612%	$269.7846	$269.78	$269.80	$269.80
Purchase #4	$54.27	3.251%	$56.0343	$56.03	$56.05	$56.00
Purchase #5	$10.86	3.421%	$11.2315	$11.23	$11.25	$11.20
Purchase #6	$231.61	10.311%	$255.4913	$255.49	$255.50	$255.50
Purchase #7	$168.68	9.528%	$184.7518	$184.75	$184.75	$184.80
7 purchase totals =	$786.45		$862.2438	$862.23	$862.30	$862.20