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	$77.93	7.702%	$83.9322	$83.93	$83.95	$83.90
Purchase #2	$17.37	3.742%	$18.02	$18.02	$18.00	$18.00
Purchase #3	$235.96	8.414%	$255.8137	$255.81	$255.80	$255.80
Purchase #4	$171.60	12.106%	$192.3739	$192.37	$192.35	$192.40
Purchase #5	$107.68	10.382%	$118.8593	$118.86	$118.85	$118.90
Purchase #6	$100.33	11.174%	$111.5409	$111.54	$111.55	$111.50
Purchase #7	$247.61	5.257%	$260.6269	$260.63	$260.65	$260.60
7 purchase totals =	$958.48		$1,041.1669	$1,041.16	$1,041.15	$1,041.10