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	$59.75	10.874%	$66.2472	$66.25	$66.25	$66.20
Purchase #2	$183.70	10.811%	$203.5598	$203.56	$203.55	$203.60
Purchase #3	$235.38	12.187%	$264.0658	$264.07	$264.05	$264.10
Purchase #4	$173.28	7.111%	$185.6019	$185.60	$185.60	$185.60
Purchase #5	$139.87	4.697%	$146.4397	$146.44	$146.45	$146.40
Purchase #6	$114.79	3.274%	$118.5482	$118.55	$118.55	$118.50
Purchase #7	$218.65	10.469%	$241.5405	$241.54	$241.55	$241.50
7 purchase totals =	$1,125.42		$1,226.0031	$1,226.01	$1,226.00	$1,225.90