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	$245.71	5.766%	$259.8776	$259.88	$259.90	$259.90
Purchase #2	$155.56	10.862%	$172.4569	$172.46	$172.45	$172.50
Purchase #3	$21.34	7.436%	$22.9268	$22.93	$22.95	$22.90
Purchase #4	$133.43	9.408%	$145.9831	$145.98	$146.00	$146.00
Purchase #5	$97.64	7.651%	$105.1104	$105.11	$105.10	$105.10
Purchase #6	$105.74	8.636%	$114.8717	$114.87	$114.85	$114.90
Purchase #7	$83.75	10.171%	$92.2682	$92.27	$92.25	$92.30
7 purchase totals =	$843.17		$913.4947	$913.50	$913.50	$913.60