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	$77.44	6.114%	$82.1747	$82.17	$82.15	$82.20
Purchase #2	$148.77	10.553%	$164.4697	$164.47	$164.45	$164.50
Purchase #3	$115.61	11.401%	$128.7907	$128.79	$128.80	$128.80
Purchase #4	$112.77	13.493%	$127.9861	$127.99	$128.00	$128.00
Purchase #5	$19.91	3.832%	$20.673	$20.67	$20.65	$20.70
Purchase #6	$248.87	5.651%	$262.9336	$262.93	$262.95	$262.90
Purchase #7	$140.67	7.651%	$151.4327	$151.43	$151.45	$151.40
7 purchase totals =	$864.04		$938.4605	$938.45	$938.45	$938.50