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	$105.45	5.499%	$111.2487	$111.25	$111.25	$111.20
Purchase #2	$29.78	10.330%	$32.8563	$32.86	$32.85	$32.90
Purchase #3	$68.51	4.852%	$71.8341	$71.83	$71.85	$71.80
Purchase #4	$94.68	10.270%	$104.4036	$104.40	$104.40	$104.40
Purchase #5	$191.94	5.853%	$203.1742	$203.17	$203.15	$203.20
Purchase #6	$43.29	13.711%	$49.2255	$49.23	$49.25	$49.20
Purchase #7	$15.29	11.473%	$17.0442	$17.04	$17.05	$17.00
7 purchase totals =	$548.94		$589.7866	$589.78	$589.80	$589.70