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	$123.87	9.337%	$135.4357	$135.44	$135.45	$135.40
Purchase #2	$244.25	9.105%	$266.489	$266.49	$266.50	$266.50
Purchase #3	$17.67	5.182%	$18.5857	$18.59	$18.60	$18.60
Purchase #4	$222.83	13.589%	$253.1104	$253.11	$253.10	$253.10
Purchase #5	$189.70	4.746%	$198.7032	$198.70	$198.70	$198.70
Purchase #6	$100.82	8.444%	$109.3332	$109.33	$109.35	$109.30
Purchase #7	$132.45	10.172%	$145.9228	$145.92	$145.90	$145.90
7 purchase totals =	$1,031.59		$1,127.5800	$1,127.58	$1,127.60	$1,127.50