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	$223.67	12.480%	$251.584	$251.58	$251.60	$251.60
Purchase #2	$208.35	10.763%	$230.7747	$230.77	$230.75	$230.80
Purchase #3	$36.70	8.598%	$39.8555	$39.86	$39.85	$39.90
Purchase #4	$128.36	13.727%	$145.98	$145.98	$146.00	$146.00
Purchase #5	$159.42	9.382%	$174.3768	$174.38	$174.40	$174.40
Purchase #6	$41.64	4.300%	$43.4305	$43.43	$43.45	$43.40
Purchase #7	$40.72	12.841%	$45.9489	$45.95	$45.95	$45.90
7 purchase totals =	$838.86		$931.9504	$931.95	$932.00	$932.00