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	$27.44	13.422%	$31.123	$31.12	$31.10	$31.10
Purchase #2	$246.69	10.631%	$272.9156	$272.92	$272.90	$272.90
Purchase #3	$205.62	12.160%	$230.6234	$230.62	$230.60	$230.60
Purchase #4	$211.62	4.791%	$221.7587	$221.76	$221.75	$221.80
Purchase #5	$59.95	3.209%	$61.8738	$61.87	$61.85	$61.90
Purchase #6	$184.71	6.472%	$196.6644	$196.66	$196.65	$196.70
Purchase #7	$49.32	11.261%	$54.8739	$54.87	$54.85	$54.90
7 purchase totals =	$985.35		$1,069.8328	$1,069.82	$1,069.70	$1,069.90