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	$199.35	12.156%	$223.583	$223.58	$223.60	$223.60
Purchase #2	$153.72	12.532%	$172.9842	$172.98	$173.00	$173.00
Purchase #3	$237.90	7.536%	$255.8281	$255.83	$255.85	$255.80
Purchase #4	$27.30	13.464%	$30.9757	$30.98	$31.00	$31.00
Purchase #5	$49.49	10.290%	$54.5825	$54.58	$54.60	$54.60
Purchase #6	$62.28	4.839%	$65.2937	$65.29	$65.30	$65.30
Purchase #7	$70.35	12.153%	$78.8996	$78.90	$78.90	$78.90
7 purchase totals =	$800.39		$882.1468	$882.14	$882.25	$882.20