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	$24.98	12.661%	$28.1427	$28.14	$28.15	$28.10
Purchase #2	$9.85	4.374%	$10.2808	$10.28	$10.30	$10.30
Purchase #3	$90.94	12.574%	$102.3748	$102.37	$102.35	$102.40
Purchase #4	$53.87	4.233%	$56.1503	$56.15	$56.15	$56.20
Purchase #5	$117.94	10.366%	$130.1657	$130.17	$130.15	$130.20
Purchase #6	$233.41	9.722%	$256.1021	$256.10	$256.10	$256.10
Purchase #7	$123.83	10.146%	$136.3938	$136.39	$136.40	$136.40
7 purchase totals =	$654.82		$719.6102	$719.60	$719.60	$719.70