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	$94.40	6.324%	$100.3699	$100.37	$100.35	$100.40
Purchase #2	$56.95	5.173%	$59.896	$59.90	$59.90	$59.90
Purchase #3	$83.29	4.621%	$87.1388	$87.14	$87.15	$87.10
Purchase #4	$34.93	8.817%	$38.0098	$38.01	$38.00	$38.00
Purchase #5	$165.43	12.851%	$186.6894	$186.69	$186.70	$186.70
Purchase #6	$151.31	11.335%	$168.461	$168.46	$168.45	$168.50
Purchase #7	$16.60	12.557%	$18.6845	$18.68	$18.70	$18.70
7 purchase totals =	$602.91		$659.2494	$659.25	$659.25	$659.30