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	$154.80	10.726%	$171.4038	$171.40	$171.40	$171.40
Purchase #2	$107.37	8.641%	$116.6478	$116.65	$116.65	$116.60
Purchase #3	$75.27	13.705%	$85.5858	$85.59	$85.60	$85.60
Purchase #4	$158.52	8.670%	$172.2637	$172.26	$172.25	$172.30
Purchase #5	$38.32	11.671%	$42.7923	$42.79	$42.80	$42.80
Purchase #6	$113.65	13.302%	$128.7677	$128.77	$128.75	$128.80
Purchase #7	$120.39	4.692%	$126.0387	$126.04	$126.05	$126.00
7 purchase totals =	$768.32		$843.4998	$843.50	$843.50	$843.50