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	$111.37	10.787%	$123.3835	$123.38	$123.40	$123.40
Purchase #2	$198.85	3.396%	$205.6029	$205.60	$205.60	$205.60
Purchase #3	$202.49	13.627%	$230.0833	$230.08	$230.10	$230.10
Purchase #4	$77.83	11.708%	$86.9423	$86.94	$86.95	$86.90
Purchase #5	$177.47	5.273%	$186.828	$186.83	$186.85	$186.80
Purchase #6	$143.55	6.756%	$153.2482	$153.25	$153.25	$153.20
Purchase #7	$28.72	8.131%	$31.0552	$31.06	$31.05	$31.10
7 purchase totals =	$940.28		$1,017.1434	$1,017.14	$1,017.20	$1,017.10