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	$49.76	10.161%	$54.8161	$54.82	$54.80	$54.80
Purchase #2	$80.38	9.370%	$87.9116	$87.91	$87.90	$87.90
Purchase #3	$160.60	8.209%	$173.7837	$173.78	$173.80	$173.80
Purchase #4	$213.34	8.234%	$230.9064	$230.91	$230.90	$230.90
Purchase #5	$143.45	9.339%	$156.8468	$156.85	$156.85	$156.80
Purchase #6	$49.72	3.600%	$51.5099	$51.51	$51.50	$51.50
Purchase #7	$99.90	12.385%	$112.2726	$112.27	$112.25	$112.30
7 purchase totals =	$797.15		$868.0471	$868.05	$868.00	$868.00