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	$28.60	6.844%	$30.5574	$30.56	$30.55	$30.60
Purchase #2	$225.28	3.680%	$233.5703	$233.57	$233.55	$233.60
Purchase #3	$244.72	3.246%	$252.6636	$252.66	$252.65	$252.70
Purchase #4	$78.84	10.136%	$86.8312	$86.83	$86.85	$86.80
Purchase #5	$30.42	7.309%	$32.6434	$32.64	$32.65	$32.60
Purchase #6	$116.67	13.358%	$132.2548	$132.25	$132.25	$132.30
Purchase #7	$96.77	4.259%	$100.8914	$100.89	$100.90	$100.90
7 purchase totals =	$821.30		$869.4121	$869.40	$869.40	$869.50