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	$11.60	10.626%	$12.8326	$12.83	$12.85	$12.80
Purchase #2	$217.95	9.550%	$238.7642	$238.76	$238.75	$238.80
Purchase #3	$139.89	6.164%	$148.5128	$148.51	$148.50	$148.50
Purchase #4	$117.37	12.839%	$132.4391	$132.44	$132.45	$132.40
Purchase #5	$232.45	8.270%	$251.6736	$251.67	$251.65	$251.70
Purchase #6	$145.33	13.188%	$164.4961	$164.50	$164.50	$164.50
Purchase #7	$206.44	11.684%	$230.5604	$230.56	$230.55	$230.60
7 purchase totals =	$1,071.03		$1,179.2788	$1,179.27	$1,179.25	$1,179.30