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	$80.42	12.770%	$90.6896	$90.69	$90.70	$90.70
Purchase #2	$229.94	3.536%	$238.0707	$238.07	$238.05	$238.10
Purchase #3	$241.85	8.135%	$261.5245	$261.52	$261.50	$261.50
Purchase #4	$107.98	3.152%	$111.3835	$111.38	$111.40	$111.40
Purchase #5	$86.67	3.750%	$89.9201	$89.92	$89.90	$89.90
Purchase #6	$59.76	10.329%	$65.9326	$65.93	$65.95	$65.90
Purchase #7	$14.43	5.691%	$15.2512	$15.25	$15.25	$15.30
7 purchase totals =	$821.05		$872.7722	$872.76	$872.75	$872.80