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	$172.40	6.300%	$183.2612	$183.26	$183.25	$183.30
Purchase #2	$118.72	6.695%	$126.6683	$126.67	$126.65	$126.70
Purchase #3	$99.46	5.182%	$104.614	$104.61	$104.60	$104.60
Purchase #4	$124.90	11.207%	$138.8975	$138.90	$138.90	$138.90
Purchase #5	$173.85	9.587%	$190.517	$190.52	$190.50	$190.50
Purchase #6	$71.27	10.236%	$78.5652	$78.57	$78.55	$78.60
Purchase #7	$41.40	5.545%	$43.6956	$43.70	$43.70	$43.70
7 purchase totals =	$802.00		$866.2188	$866.23	$866.15	$866.30