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	$215.36	10.570%	$238.1236	$238.12	$238.10	$238.10
Purchase #2	$137.28	11.534%	$153.1139	$153.11	$153.10	$153.10
Purchase #3	$103.71	7.481%	$111.4685	$111.47	$111.45	$111.50
Purchase #4	$11.44	3.583%	$11.8499	$11.85	$11.85	$11.80
Purchase #5	$236.47	9.230%	$258.2962	$258.30	$258.30	$258.30
Purchase #6	$92.90	10.699%	$102.8394	$102.84	$102.85	$102.80
Purchase #7	$153.59	13.284%	$173.9929	$173.99	$174.00	$174.00
7 purchase totals =	$950.75		$1,049.6844	$1,049.68	$1,049.65	$1,049.60