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	$47.73	8.597%	$51.8333	$51.83	$51.85	$51.80
Purchase #2	$247.31	13.555%	$280.8329	$280.83	$280.85	$280.80
Purchase #3	$44.92	3.308%	$46.406	$46.41	$46.40	$46.40
Purchase #4	$17.86	4.104%	$18.593	$18.59	$18.60	$18.60
Purchase #5	$99.52	6.461%	$105.95	$105.95	$105.95	$106.00
Purchase #6	$119.57	5.553%	$126.2097	$126.21	$126.20	$126.20
Purchase #7	$11.30	9.700%	$12.3961	$12.40	$12.40	$12.40
7 purchase totals =	$588.21		$642.2210	$642.22	$642.25	$642.20