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	$70.82	13.787%	$80.584	$80.58	$80.60	$80.60
Purchase #2	$115.52	10.378%	$127.5087	$127.51	$127.50	$127.50
Purchase #3	$66.65	5.273%	$70.1645	$70.16	$70.15	$70.20
Purchase #4	$28.87	3.411%	$29.8548	$29.85	$29.85	$29.90
Purchase #5	$127.85	8.174%	$138.3005	$138.30	$138.30	$138.30
Purchase #6	$35.43	10.531%	$39.1611	$39.16	$39.15	$39.20
Purchase #7	$178.27	11.541%	$198.8441	$198.84	$198.85	$198.80
7 purchase totals =	$623.41		$684.4177	$684.40	$684.40	$684.50