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	$12.77	4.779%	$13.3803	$13.38	$13.40	$13.40
Purchase #2	$99.85	8.757%	$108.5939	$108.59	$108.60	$108.60
Purchase #3	$29.32	12.379%	$32.9495	$32.95	$32.95	$32.90
Purchase #4	$19.28	3.620%	$19.9779	$19.98	$20.00	$20.00
Purchase #5	$152.71	13.436%	$173.2281	$173.23	$173.25	$173.20
Purchase #6	$196.72	13.203%	$222.6929	$222.69	$222.70	$222.70
Purchase #7	$172.37	5.306%	$181.516	$181.52	$181.50	$181.50
7 purchase totals =	$683.02		$752.3386	$752.34	$752.40	$752.30