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	$167.52	3.570%	$173.5005	$173.50	$173.50	$173.50
Purchase #2	$148.57	11.793%	$166.0909	$166.09	$166.10	$166.10
Purchase #3	$32.34	3.204%	$33.3762	$33.38	$33.40	$33.40
Purchase #4	$246.66	10.518%	$272.6037	$272.60	$272.60	$272.60
Purchase #5	$72.71	8.239%	$78.7006	$78.70	$78.70	$78.70
Purchase #6	$22.37	11.397%	$24.9195	$24.92	$24.90	$24.90
Purchase #7	$214.72	12.159%	$240.8278	$240.83	$240.85	$240.80
7 purchase totals =	$904.89		$990.0192	$990.02	$990.05	$990.00