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	$28.90	12.172%	$32.4177	$32.42	$32.40	$32.40
Purchase #2	$158.81	11.197%	$176.592	$176.59	$176.60	$176.60
Purchase #3	$14.41	10.336%	$15.8994	$15.90	$15.90	$15.90
Purchase #4	$126.93	12.276%	$142.5119	$142.51	$142.50	$142.50
Purchase #5	$112.71	13.295%	$127.6948	$127.69	$127.70	$127.70
Purchase #6	$51.74	9.147%	$56.4727	$56.47	$56.45	$56.50
Purchase #7	$187.31	9.811%	$205.687	$205.69	$205.70	$205.70
7 purchase totals =	$680.81		$757.2755	$757.27	$757.25	$757.30