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	$16.39	11.324%	$18.246	$18.25	$18.25	$18.20
Purchase #2	$185.89	10.504%	$205.4159	$205.42	$205.40	$205.40
Purchase #3	$136.82	4.861%	$143.4708	$143.47	$143.45	$143.50
Purchase #4	$164.78	7.196%	$176.6376	$176.64	$176.65	$176.60
Purchase #5	$114.53	11.532%	$127.7376	$127.74	$127.75	$127.70
Purchase #6	$122.25	4.503%	$127.7549	$127.75	$127.75	$127.80
Purchase #7	$18.27	4.136%	$19.0256	$19.03	$19.05	$19.00
7 purchase totals =	$758.93		$818.2884	$818.30	$818.30	$818.20