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	$80.37	3.151%	$82.9025	$82.90	$82.90	$82.90
Purchase #2	$231.65	10.297%	$255.503	$255.50	$255.50	$255.50
Purchase #3	$136.85	13.176%	$154.8814	$154.88	$154.90	$154.90
Purchase #4	$52.32	7.592%	$56.2921	$56.29	$56.30	$56.30
Purchase #5	$63.60	5.194%	$66.9034	$66.90	$66.90	$66.90
Purchase #6	$16.97	13.784%	$19.3091	$19.31	$19.30	$19.30
Purchase #7	$16.78	12.870%	$18.9396	$18.94	$18.95	$18.90
7 purchase totals =	$598.54		$654.7311	$654.72	$654.75	$654.70