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	$12.45	6.703%	$13.2845	$13.28	$13.30	$13.30
Purchase #2	$37.43	11.446%	$41.7142	$41.71	$41.70	$41.70
Purchase #3	$182.37	12.561%	$205.2775	$205.28	$205.30	$205.30
Purchase #4	$224.87	12.760%	$253.5634	$253.56	$253.55	$253.60
Purchase #5	$213.39	3.691%	$221.2662	$221.27	$221.25	$221.30
Purchase #6	$57.37	4.866%	$60.1616	$60.16	$60.15	$60.20
Purchase #7	$153.81	12.217%	$172.601	$172.60	$172.60	$172.60
7 purchase totals =	$881.69		$967.8684	$967.86	$967.85	$968.00