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	$159.27	10.646%	$176.2259	$176.23	$176.25	$176.20
Purchase #2	$114.87	5.235%	$120.8834	$120.88	$120.90	$120.90
Purchase #3	$204.98	12.574%	$230.7542	$230.75	$230.75	$230.80
Purchase #4	$249.91	12.189%	$280.3715	$280.37	$280.35	$280.40
Purchase #5	$75.72	3.379%	$78.2786	$78.28	$78.30	$78.30
Purchase #6	$36.61	12.733%	$41.2716	$41.27	$41.25	$41.30
Purchase #7	$49.79	8.515%	$54.0296	$54.03	$54.05	$54.00
7 purchase totals =	$891.15		$981.8148	$981.81	$981.85	$981.90