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	$137.37	12.692%	$154.805	$154.81	$154.80	$154.80
Purchase #2	$182.55	8.124%	$197.3804	$197.38	$197.40	$197.40
Purchase #3	$193.71	12.527%	$217.9761	$217.98	$218.00	$218.00
Purchase #4	$45.86	5.727%	$48.4864	$48.49	$48.50	$48.50
Purchase #5	$205.78	13.262%	$233.0705	$233.07	$233.05	$233.10
Purchase #6	$106.62	11.158%	$118.5167	$118.52	$118.50	$118.50
Purchase #7	$131.89	10.592%	$145.8598	$145.86	$145.85	$145.90
7 purchase totals =	$1,003.78		$1,116.0949	$1,116.11	$1,116.10	$1,116.20