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	$16.99	5.295%	$17.8896	$17.89	$17.90	$17.90
Purchase #2	$129.91	7.274%	$139.3597	$139.36	$139.35	$139.40
Purchase #3	$119.58	6.285%	$127.0956	$127.10	$127.10	$127.10
Purchase #4	$54.91	11.564%	$61.2598	$61.26	$61.25	$61.30
Purchase #5	$134.87	12.460%	$151.6748	$151.67	$151.65	$151.70
Purchase #6	$170.54	10.515%	$188.4723	$188.47	$188.45	$188.50
Purchase #7	$111.35	4.250%	$116.0824	$116.08	$116.10	$116.10
7 purchase totals =	$738.15		$801.8342	$801.83	$801.80	$802.00