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	$81.46	10.316%	$89.8634	$89.86	$89.85	$89.90
Purchase #2	$43.31	7.168%	$46.4145	$46.41	$46.40	$46.40
Purchase #3	$146.76	8.248%	$158.8648	$158.86	$158.85	$158.90
Purchase #4	$231.90	13.661%	$263.5799	$263.58	$263.60	$263.60
Purchase #5	$229.53	5.407%	$241.9407	$241.94	$241.95	$241.90
Purchase #6	$94.71	11.579%	$105.6765	$105.68	$105.70	$105.70
Purchase #7	$21.68	6.322%	$23.0506	$23.05	$23.05	$23.10
7 purchase totals =	$849.35		$929.3904	$929.38	$929.40	$929.50