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	$108.72	9.178%	$118.6983	$118.70	$118.70	$118.70
Purchase #2	$19.68	3.575%	$20.3836	$20.38	$20.40	$20.40
Purchase #3	$92.32	13.816%	$105.0749	$105.07	$105.05	$105.10
Purchase #4	$138.89	8.679%	$150.9443	$150.94	$150.95	$150.90
Purchase #5	$86.89	6.464%	$92.5066	$92.51	$92.50	$92.50
Purchase #6	$18.65	9.332%	$20.3904	$20.39	$20.40	$20.40
Purchase #7	$46.92	5.839%	$49.6597	$49.66	$49.65	$49.70
7 purchase totals =	$512.07		$557.6578	$557.65	$557.65	$557.70