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	$158.27	13.416%	$179.5035	$179.50	$179.50	$179.50
Purchase #2	$142.93	6.272%	$151.8946	$151.89	$151.90	$151.90
Purchase #3	$101.81	3.434%	$105.3062	$105.31	$105.30	$105.30
Purchase #4	$39.26	13.189%	$44.438	$44.44	$44.45	$44.40
Purchase #5	$108.57	3.631%	$112.5122	$112.51	$112.50	$112.50
Purchase #6	$116.26	6.398%	$123.6983	$123.70	$123.70	$123.70
Purchase #7	$236.54	10.445%	$261.2466	$261.25	$261.25	$261.20
7 purchase totals =	$903.64		$978.5994	$978.60	$978.60	$978.50