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	$23.41	7.323%	$25.1243	$25.12	$25.10	$25.10
Purchase #2	$104.54	11.845%	$116.9228	$116.92	$116.90	$116.90
Purchase #3	$237.72	10.173%	$261.9033	$261.90	$261.90	$261.90
Purchase #4	$51.97	13.526%	$58.9995	$59.00	$59.00	$59.00
Purchase #5	$16.42	5.508%	$17.3244	$17.32	$17.30	$17.30
Purchase #6	$105.42	5.555%	$111.2761	$111.28	$111.30	$111.30
Purchase #7	$26.64	11.200%	$29.6237	$29.62	$29.60	$29.60
7 purchase totals =	$566.12		$621.1741	$621.16	$621.10	$621.10