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	$89.82	10.853%	$99.5682	$99.57	$99.55	$99.60
Purchase #2	$103.60	4.656%	$108.4236	$108.42	$108.40	$108.40
Purchase #3	$123.62	7.490%	$132.8791	$132.88	$132.90	$132.90
Purchase #4	$99.91	9.181%	$109.0827	$109.08	$109.10	$109.10
Purchase #5	$116.53	10.456%	$128.7144	$128.71	$128.70	$128.70
Purchase #6	$128.91	8.170%	$139.4419	$139.44	$139.45	$139.40
Purchase #7	$8.97	5.733%	$9.4843	$9.48	$9.50	$9.50
7 purchase totals =	$671.36		$727.5942	$727.58	$727.60	$727.60