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	$33.52	11.602%	$37.409	$37.41	$37.40	$37.40
Purchase #2	$32.65	4.669%	$34.1744	$34.17	$34.15	$34.20
Purchase #3	$47.78	10.140%	$52.6249	$52.62	$52.60	$52.60
Purchase #4	$239.50	6.670%	$255.4747	$255.47	$255.45	$255.50
Purchase #5	$99.29	12.848%	$112.0468	$112.05	$112.05	$112.00
Purchase #6	$9.95	6.175%	$10.5644	$10.56	$10.55	$10.60
Purchase #7	$132.59	8.805%	$144.2645	$144.26	$144.25	$144.30
7 purchase totals =	$595.28		$646.5587	$646.54	$646.45	$646.60