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	$170.76	6.870%	$182.4912	$182.49	$182.50	$182.50
Purchase #2	$112.25	5.509%	$118.4339	$118.43	$118.45	$118.40
Purchase #3	$173.35	11.106%	$192.6023	$192.60	$192.60	$192.60
Purchase #4	$11.49	10.448%	$12.6905	$12.69	$12.70	$12.70
Purchase #5	$75.84	8.496%	$82.2834	$82.28	$82.30	$82.30
Purchase #6	$164.56	9.735%	$180.5799	$180.58	$180.60	$180.60
Purchase #7	$210.53	6.600%	$224.425	$224.43	$224.45	$224.40
7 purchase totals =	$918.78		$993.5062	$993.50	$993.60	$993.50