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	$158.45	9.552%	$173.5851	$173.59	$173.60	$173.60
Purchase #2	$78.29	6.872%	$83.6701	$83.67	$83.65	$83.70
Purchase #3	$56.67	12.741%	$63.8903	$63.89	$63.90	$63.90
Purchase #4	$200.44	5.786%	$212.0375	$212.04	$212.05	$212.00
Purchase #5	$85.40	5.475%	$90.0757	$90.08	$90.10	$90.10
Purchase #6	$230.51	7.756%	$248.3884	$248.39	$248.40	$248.40
Purchase #7	$45.90	8.641%	$49.8662	$49.87	$49.85	$49.90
7 purchase totals =	$855.66		$921.5133	$921.53	$921.55	$921.60