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	$120.96	5.663%	$127.81	$127.81	$127.80	$127.80
Purchase #2	$126.64	6.278%	$134.5905	$134.59	$134.60	$134.60
Purchase #3	$68.78	8.790%	$74.8258	$74.83	$74.85	$74.80
Purchase #4	$112.30	5.384%	$118.3462	$118.35	$118.35	$118.30
Purchase #5	$76.38	12.118%	$85.6357	$85.64	$85.65	$85.60
Purchase #6	$177.72	10.548%	$196.4659	$196.47	$196.45	$196.50
Purchase #7	$236.40	9.182%	$258.1062	$258.11	$258.10	$258.10
7 purchase totals =	$919.18		$995.7803	$995.80	$995.80	$995.70