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	$66.55	6.139%	$70.6355	$70.64	$70.65	$70.60
Purchase #2	$217.43	10.676%	$240.6428	$240.64	$240.65	$240.60
Purchase #3	$89.86	4.105%	$93.5488	$93.55	$93.55	$93.50
Purchase #4	$219.35	11.358%	$244.2638	$244.26	$244.25	$244.30
Purchase #5	$206.68	9.307%	$225.9157	$225.92	$225.90	$225.90
Purchase #6	$83.25	8.240%	$90.1098	$90.11	$90.10	$90.10
Purchase #7	$108.81	4.189%	$113.3681	$113.37	$113.35	$113.40
7 purchase totals =	$991.93		$1,078.4845	$1,078.49	$1,078.45	$1,078.40