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	$12.30	7.589%	$13.2334	$13.23	$13.25	$13.20
Purchase #2	$171.43	4.287%	$178.7792	$178.78	$178.80	$178.80
Purchase #3	$136.25	10.269%	$150.2415	$150.24	$150.25	$150.20
Purchase #4	$250.66	11.493%	$279.4684	$279.47	$279.45	$279.50
Purchase #5	$244.57	5.420%	$257.8257	$257.83	$257.85	$257.80
Purchase #6	$217.52	4.230%	$226.7211	$226.72	$226.70	$226.70
Purchase #7	$74.97	5.227%	$78.8887	$78.89	$78.90	$78.90
7 purchase totals =	$1,107.70		$1,185.1580	$1,185.16	$1,185.20	$1,185.10