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	$60.44	9.223%	$66.0144	$66.01	$66.00	$66.00
Purchase #2	$33.37	4.530%	$34.8817	$34.88	$34.90	$34.90
Purchase #3	$127.68	3.793%	$132.5229	$132.52	$132.50	$132.50
Purchase #4	$49.92	8.348%	$54.0873	$54.09	$54.10	$54.10
Purchase #5	$102.69	11.294%	$114.2878	$114.29	$114.30	$114.30
Purchase #6	$117.35	9.219%	$128.1685	$128.17	$128.15	$128.20
Purchase #7	$37.87	7.820%	$40.8314	$40.83	$40.85	$40.80
7 purchase totals =	$529.32		$570.7940	$570.79	$570.80	$570.80