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	$133.68	13.478%	$151.6974	$151.70	$151.70	$151.70
Purchase #2	$28.72	6.381%	$30.5526	$30.55	$30.55	$30.60
Purchase #3	$95.50	4.308%	$99.6141	$99.61	$99.60	$99.60
Purchase #4	$27.59	4.624%	$28.8658	$28.87	$28.85	$28.90
Purchase #5	$138.91	11.810%	$155.3153	$155.32	$155.30	$155.30
Purchase #6	$181.71	3.383%	$187.8572	$187.86	$187.85	$187.90
Purchase #7	$108.86	9.484%	$119.1843	$119.18	$119.20	$119.20
7 purchase totals =	$714.97		$773.0867	$773.09	$773.05	$773.20