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	$144.51	8.162%	$156.3049	$156.30	$156.30	$156.30
Purchase #2	$38.79	4.614%	$40.5798	$40.58	$40.60	$40.60
Purchase #3	$41.32	13.332%	$46.8288	$46.83	$46.85	$46.80
Purchase #4	$51.64	12.506%	$58.0981	$58.10	$58.10	$58.10
Purchase #5	$159.98	8.383%	$173.3911	$173.39	$173.40	$173.40
Purchase #6	$96.71	4.654%	$101.2109	$101.21	$101.20	$101.20
Purchase #7	$47.66	10.227%	$52.5342	$52.53	$52.55	$52.50
7 purchase totals =	$580.61		$628.9478	$628.94	$629.00	$628.90