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	$80.61	10.819%	$89.3312	$89.33	$89.35	$89.30
Purchase #2	$129.55	12.651%	$145.9394	$145.94	$145.95	$145.90
Purchase #3	$62.38	5.329%	$65.7042	$65.70	$65.70	$65.70
Purchase #4	$112.30	3.771%	$116.5348	$116.53	$116.55	$116.50
Purchase #5	$51.95	4.120%	$54.0903	$54.09	$54.10	$54.10
Purchase #6	$29.94	12.157%	$33.5798	$33.58	$33.60	$33.60
Purchase #7	$10.35	8.711%	$11.2516	$11.25	$11.25	$11.30
7 purchase totals =	$477.08		$516.4313	$516.42	$516.50	$516.40