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	$220.40	4.466%	$230.2431	$230.24	$230.25	$230.20
Purchase #2	$30.42	6.608%	$32.4302	$32.43	$32.45	$32.40
Purchase #3	$40.54	5.192%	$42.6448	$42.64	$42.65	$42.60
Purchase #4	$123.96	10.249%	$136.6647	$136.66	$136.65	$136.70
Purchase #5	$41.75	12.349%	$46.9057	$46.91	$46.90	$46.90
Purchase #6	$138.27	3.452%	$143.0431	$143.04	$143.05	$143.00
Purchase #7	$137.27	5.591%	$144.9448	$144.94	$144.95	$144.90
7 purchase totals =	$732.61		$776.8764	$776.86	$776.90	$776.70