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	$155.33	11.462%	$173.1339	$173.13	$173.15	$173.10
Purchase #2	$115.62	9.777%	$126.9242	$126.92	$126.90	$126.90
Purchase #3	$193.69	12.541%	$217.9807	$217.98	$218.00	$218.00
Purchase #4	$140.61	7.761%	$151.5227	$151.52	$151.50	$151.50
Purchase #5	$119.62	10.576%	$132.271	$132.27	$132.25	$132.30
Purchase #6	$106.25	7.665%	$114.3941	$114.39	$114.40	$114.40
Purchase #7	$48.38	10.332%	$53.3786	$53.38	$53.40	$53.40
7 purchase totals =	$879.50		$969.6052	$969.59	$969.60	$969.60