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	$90.46	13.737%	$102.8865	$102.89	$102.90	$102.90
Purchase #2	$118.97	9.632%	$130.4292	$130.43	$130.45	$130.40
Purchase #3	$46.51	4.601%	$48.6499	$48.65	$48.65	$48.60
Purchase #4	$226.62	13.725%	$257.7236	$257.72	$257.70	$257.70
Purchase #5	$90.90	13.143%	$102.847	$102.85	$102.85	$102.80
Purchase #6	$191.27	13.152%	$216.4258	$216.43	$216.45	$216.40
Purchase #7	$40.91	8.680%	$44.461	$44.46	$44.45	$44.50
7 purchase totals =	$805.64		$903.4230	$903.43	$903.45	$903.30