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	$74.45	5.838%	$78.7964	$78.80	$78.80	$78.80
Purchase #2	$46.79	11.118%	$51.9921	$51.99	$52.00	$52.00
Purchase #3	$104.66	11.414%	$116.6059	$116.61	$116.60	$116.60
Purchase #4	$52.75	4.218%	$54.975	$54.98	$55.00	$55.00
Purchase #5	$173.86	9.440%	$190.2724	$190.27	$190.25	$190.30
Purchase #6	$126.91	3.422%	$131.2529	$131.25	$131.25	$131.30
Purchase #7	$38.67	12.763%	$43.6055	$43.61	$43.60	$43.60
7 purchase totals =	$618.09		$667.5002	$667.51	$667.50	$667.60