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	$211.51	5.396%	$222.9231	$222.92	$222.90	$222.90
Purchase #2	$205.65	13.859%	$234.151	$234.15	$234.15	$234.20
Purchase #3	$123.30	3.195%	$127.2394	$127.24	$127.25	$127.20
Purchase #4	$48.30	12.783%	$54.4742	$54.47	$54.45	$54.50
Purchase #5	$193.45	10.684%	$214.1182	$214.12	$214.10	$214.10
Purchase #6	$195.33	5.403%	$205.8837	$205.88	$205.90	$205.90
Purchase #7	$131.75	11.264%	$146.5903	$146.59	$146.60	$146.60
7 purchase totals =	$1,109.29		$1,205.3799	$1,205.37	$1,205.35	$1,205.40