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	$249.55	7.309%	$267.7896	$267.79	$267.80	$267.80
Purchase #2	$244.61	11.388%	$272.4662	$272.47	$272.45	$272.50
Purchase #3	$178.75	3.832%	$185.5997	$185.60	$185.60	$185.60
Purchase #4	$153.58	4.693%	$160.7875	$160.79	$160.80	$160.80
Purchase #5	$92.27	11.773%	$103.1329	$103.13	$103.15	$103.10
Purchase #6	$72.25	11.718%	$80.7163	$80.72	$80.70	$80.70
Purchase #7	$127.60	9.340%	$139.5178	$139.52	$139.50	$139.50
7 purchase totals =	$1,118.61		$1,210.0100	$1,210.02	$1,210.00	$1,210.00