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	$5.30	8.398%	$5.7451	$5.75	$5.75	$5.70
Purchase #2	$137.55	8.221%	$148.858	$148.86	$148.85	$148.90
Purchase #3	$89.90	13.186%	$101.7542	$101.75	$101.75	$101.80
Purchase #4	$139.81	13.341%	$158.4621	$158.46	$158.45	$158.50
Purchase #5	$54.64	13.201%	$61.853	$61.85	$61.85	$61.90
Purchase #6	$241.94	6.866%	$258.5516	$258.55	$258.55	$258.60
Purchase #7	$135.90	11.508%	$151.5394	$151.54	$151.55	$151.50
7 purchase totals =	$805.04		$886.7634	$886.76	$886.75	$886.90