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	$166.55	5.822%	$176.2465	$176.25	$176.25	$176.20
Purchase #2	$86.39	9.402%	$94.5124	$94.51	$94.50	$94.50
Purchase #3	$172.29	4.769%	$180.5065	$180.51	$180.50	$180.50
Purchase #4	$146.96	8.171%	$158.9681	$158.97	$158.95	$159.00
Purchase #5	$168.97	5.757%	$178.6976	$178.70	$178.70	$178.70
Purchase #6	$12.37	9.269%	$13.5166	$13.52	$13.50	$13.50
Purchase #7	$102.37	8.606%	$111.18	$111.18	$111.20	$111.20
7 purchase totals =	$855.90		$913.6277	$913.64	$913.60	$913.60