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	$34.53	10.778%	$38.2516	$38.25	$38.25	$38.30
Purchase #2	$81.97	9.586%	$89.8276	$89.83	$89.85	$89.80
Purchase #3	$102.68	6.733%	$109.5934	$109.59	$109.60	$109.60
Purchase #4	$247.65	9.832%	$271.9989	$272.00	$272.00	$272.00
Purchase #5	$121.93	4.522%	$127.4437	$127.44	$127.45	$127.40
Purchase #6	$154.70	6.856%	$165.3062	$165.31	$165.30	$165.30
Purchase #7	$173.76	4.237%	$181.1222	$181.12	$181.10	$181.10
7 purchase totals =	$917.22		$983.5436	$983.54	$983.55	$983.50