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	$99.50	8.657%	$108.1137	$108.11	$108.10	$108.10
Purchase #2	$105.56	5.529%	$111.3964	$111.40	$111.40	$111.40
Purchase #3	$211.93	13.839%	$241.259	$241.26	$241.25	$241.30
Purchase #4	$172.53	9.733%	$189.3223	$189.32	$189.30	$189.30
Purchase #5	$37.52	10.729%	$41.5455	$41.55	$41.55	$41.50
Purchase #6	$31.71	4.746%	$33.215	$33.22	$33.20	$33.20
Purchase #7	$249.70	3.836%	$259.2785	$259.28	$259.30	$259.30
7 purchase totals =	$908.45		$984.1304	$984.14	$984.10	$984.10