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	$64.35	10.104%	$70.8519	$70.85	$70.85	$70.90
Purchase #2	$146.51	5.576%	$154.6794	$154.68	$154.70	$154.70
Purchase #3	$111.44	3.575%	$115.424	$115.42	$115.40	$115.40
Purchase #4	$74.94	5.160%	$78.8069	$78.81	$78.80	$78.80
Purchase #5	$123.44	7.171%	$132.2919	$132.29	$132.30	$132.30
Purchase #6	$48.84	11.675%	$54.5421	$54.54	$54.55	$54.50
Purchase #7	$233.44	12.858%	$263.4557	$263.46	$263.45	$263.50
7 purchase totals =	$802.96		$870.0519	$870.05	$870.05	$870.10