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	$43.66	4.497%	$45.6234	$45.62	$45.60	$45.60
Purchase #2	$144.66	9.677%	$158.6587	$158.66	$158.65	$158.70
Purchase #3	$93.52	7.862%	$100.8725	$100.87	$100.85	$100.90
Purchase #4	$108.88	8.857%	$118.5235	$118.52	$118.50	$118.50
Purchase #5	$102.57	7.697%	$110.4648	$110.46	$110.45	$110.50
Purchase #6	$29.95	10.526%	$33.1025	$33.10	$33.10	$33.10
Purchase #7	$59.31	9.256%	$64.7997	$64.80	$64.80	$64.80
7 purchase totals =	$582.55		$632.0451	$632.03	$631.95	$632.10