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	$150.78	6.527%	$160.6214	$160.62	$160.60	$160.60
Purchase #2	$194.63	10.735%	$215.5235	$215.52	$215.50	$215.50
Purchase #3	$103.90	10.861%	$115.1846	$115.18	$115.20	$115.20
Purchase #4	$101.95	9.767%	$111.9075	$111.91	$111.90	$111.90
Purchase #5	$48.32	3.239%	$49.8851	$49.89	$49.90	$49.90
Purchase #6	$149.38	4.364%	$155.8989	$155.90	$155.90	$155.90
Purchase #7	$44.41	10.592%	$49.1139	$49.11	$49.10	$49.10
7 purchase totals =	$793.37		$858.1349	$858.13	$858.10	$858.10