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	$105.94	5.551%	$111.8207	$111.82	$111.80	$111.80
Purchase #2	$164.58	11.570%	$183.6219	$183.62	$183.60	$183.60
Purchase #3	$230.64	4.585%	$241.2148	$241.21	$241.20	$241.20
Purchase #4	$79.63	11.865%	$89.0781	$89.08	$89.10	$89.10
Purchase #5	$138.54	5.849%	$146.6432	$146.64	$146.65	$146.60
Purchase #6	$100.79	10.285%	$111.1563	$111.16	$111.15	$111.20
Purchase #7	$112.96	8.446%	$122.5006	$122.50	$122.50	$122.50
7 purchase totals =	$933.08		$1,006.0356	$1,006.03	$1,006.00	$1,006.00