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	$32.80	10.242%	$36.1594	$36.16	$36.15	$36.20
Purchase #2	$188.63	6.298%	$200.5099	$200.51	$200.50	$200.50
Purchase #3	$66.86	7.579%	$71.9273	$71.93	$71.95	$71.90
Purchase #4	$214.37	4.531%	$224.0831	$224.08	$224.10	$224.10
Purchase #5	$75.29	13.469%	$85.4308	$85.43	$85.45	$85.40
Purchase #6	$86.75	5.857%	$91.8309	$91.83	$91.85	$91.80
Purchase #7	$246.36	6.178%	$261.5801	$261.58	$261.60	$261.60
7 purchase totals =	$911.06		$971.5215	$971.52	$971.60	$971.50