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	$153.82	8.474%	$166.8547	$166.85	$166.85	$166.90
Purchase #2	$208.42	9.746%	$228.7326	$228.73	$228.75	$228.70
Purchase #3	$50.46	3.228%	$52.0888	$52.09	$52.10	$52.10
Purchase #4	$36.45	11.218%	$40.539	$40.54	$40.55	$40.50
Purchase #5	$191.83	8.583%	$208.2948	$208.29	$208.30	$208.30
Purchase #6	$214.38	12.720%	$241.6491	$241.65	$241.65	$241.60
Purchase #7	$28.45	13.782%	$32.371	$32.37	$32.35	$32.40
7 purchase totals =	$883.81		$970.5300	$970.52	$970.55	$970.50