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	$162.76	12.767%	$183.5396	$183.54	$183.55	$183.50
Purchase #2	$197.81	11.237%	$220.0379	$220.04	$220.05	$220.00
Purchase #3	$56.86	12.288%	$63.847	$63.85	$63.85	$63.80
Purchase #4	$140.43	3.730%	$145.668	$145.67	$145.65	$145.70
Purchase #5	$197.82	11.852%	$221.2656	$221.27	$221.25	$221.30
Purchase #6	$83.55	8.114%	$90.3292	$90.33	$90.35	$90.30
Purchase #7	$153.31	13.446%	$173.9241	$173.92	$173.90	$173.90
7 purchase totals =	$992.54		$1,098.6114	$1,098.62	$1,098.60	$1,098.50