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	$226.38	12.716%	$255.1665	$255.17	$255.15	$255.20
Purchase #2	$49.90	4.562%	$52.1764	$52.18	$52.20	$52.20
Purchase #3	$85.92	10.812%	$95.2097	$95.21	$95.20	$95.20
Purchase #4	$13.74	11.557%	$15.3279	$15.33	$15.35	$15.30
Purchase #5	$10.77	11.261%	$11.9828	$11.98	$12.00	$12.00
Purchase #6	$224.99	13.593%	$255.5729	$255.57	$255.55	$255.60
Purchase #7	$105.30	5.546%	$111.1399	$111.14	$111.15	$111.10
7 purchase totals =	$717.00		$796.5761	$796.58	$796.60	$796.60