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	$49.25	10.750%	$54.5444	$54.54	$54.55	$54.50
Purchase #2	$221.60	4.191%	$230.8873	$230.89	$230.90	$230.90
Purchase #3	$103.82	8.163%	$112.2948	$112.29	$112.30	$112.30
Purchase #4	$91.42	13.626%	$103.8769	$103.88	$103.90	$103.90
Purchase #5	$11.55	6.766%	$12.3315	$12.33	$12.35	$12.30
Purchase #6	$36.87	8.706%	$40.0799	$40.08	$40.10	$40.10
Purchase #7	$80.60	4.381%	$84.1311	$84.13	$84.15	$84.10
7 purchase totals =	$595.11		$638.1459	$638.14	$638.25	$638.10