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	$215.88	10.671%	$238.9166	$238.92	$238.90	$238.90
Purchase #2	$135.59	13.669%	$154.1238	$154.12	$154.10	$154.10
Purchase #3	$16.90	12.429%	$19.0005	$19.00	$19.00	$19.00
Purchase #4	$39.28	8.205%	$42.5029	$42.50	$42.50	$42.50
Purchase #5	$107.65	12.799%	$121.4281	$121.43	$121.45	$121.40
Purchase #6	$40.84	4.866%	$42.8273	$42.83	$42.85	$42.80
Purchase #7	$129.40	12.358%	$145.3913	$145.39	$145.40	$145.40
7 purchase totals =	$685.54		$764.1905	$764.19	$764.20	$764.10