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	$48.91	9.244%	$53.4312	$53.43	$53.45	$53.40
Purchase #2	$172.80	8.730%	$187.8854	$187.89	$187.90	$187.90
Purchase #3	$165.82	13.491%	$188.1908	$188.19	$188.20	$188.20
Purchase #4	$43.97	8.847%	$47.86	$47.86	$47.85	$47.90
Purchase #5	$80.35	10.273%	$88.6044	$88.60	$88.60	$88.60
Purchase #6	$11.73	8.409%	$12.7164	$12.72	$12.70	$12.70
Purchase #7	$54.77	8.364%	$59.351	$59.35	$59.35	$59.40
7 purchase totals =	$578.35		$638.0392	$638.04	$638.05	$638.10