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	$15.57	4.605%	$16.287	$16.29	$16.30	$16.30
Purchase #2	$99.71	5.706%	$105.3995	$105.40	$105.40	$105.40
Purchase #3	$102.98	10.126%	$113.4078	$113.41	$113.40	$113.40
Purchase #4	$111.89	9.723%	$122.7691	$122.77	$122.75	$122.80
Purchase #5	$107.39	3.741%	$111.4075	$111.41	$111.40	$111.40
Purchase #6	$39.70	6.387%	$42.2356	$42.24	$42.25	$42.20
Purchase #7	$107.66	9.667%	$118.0675	$118.07	$118.05	$118.10
7 purchase totals =	$584.90		$629.5740	$629.59	$629.55	$629.60