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	$233.92	6.258%	$248.5587	$248.56	$248.55	$248.60
Purchase #2	$97.81	13.601%	$111.1131	$111.11	$111.10	$111.10
Purchase #3	$116.98	8.143%	$126.5057	$126.51	$126.50	$126.50
Purchase #4	$10.94	5.318%	$11.5218	$11.52	$11.50	$11.50
Purchase #5	$211.74	12.715%	$238.6627	$238.66	$238.65	$238.70
Purchase #6	$74.40	10.554%	$82.2522	$82.25	$82.25	$82.30
Purchase #7	$40.99	3.177%	$42.2923	$42.29	$42.30	$42.30
7 purchase totals =	$786.78		$860.9065	$860.90	$860.85	$861.00