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	$143.27	3.685%	$148.5495	$148.55	$148.55	$148.50
Purchase #2	$72.30	13.501%	$82.0612	$82.06	$82.05	$82.10
Purchase #3	$233.28	8.808%	$253.8273	$253.83	$253.85	$253.80
Purchase #4	$124.78	3.323%	$128.9264	$128.93	$128.95	$128.90
Purchase #5	$52.95	3.436%	$54.7694	$54.77	$54.75	$54.80
Purchase #6	$46.91	7.395%	$50.379	$50.38	$50.40	$50.40
Purchase #7	$100.63	10.638%	$111.335	$111.34	$111.35	$111.30
7 purchase totals =	$774.12		$829.8478	$829.86	$829.90	$829.80