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	$159.48	5.287%	$167.9117	$167.91	$167.90	$167.90
Purchase #2	$240.60	10.719%	$266.3899	$266.39	$266.40	$266.40
Purchase #3	$140.32	11.146%	$155.9601	$155.96	$155.95	$156.00
Purchase #4	$172.70	8.249%	$186.946	$186.95	$186.95	$186.90
Purchase #5	$114.60	7.868%	$123.6167	$123.62	$123.60	$123.60
Purchase #6	$10.88	12.493%	$12.2392	$12.24	$12.25	$12.20
Purchase #7	$151.76	4.260%	$158.225	$158.23	$158.25	$158.20
7 purchase totals =	$990.34		$1,071.2886	$1,071.30	$1,071.30	$1,071.20