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	$29.63	12.480%	$33.3278	$33.33	$33.35	$33.30
Purchase #2	$62.75	6.679%	$66.9411	$66.94	$66.95	$66.90
Purchase #3	$57.40	6.732%	$61.2642	$61.26	$61.25	$61.30
Purchase #4	$97.37	6.293%	$103.4975	$103.50	$103.50	$103.50
Purchase #5	$38.98	12.447%	$43.8318	$43.83	$43.85	$43.80
Purchase #6	$160.60	7.799%	$173.1252	$173.13	$173.15	$173.10
Purchase #7	$104.70	4.186%	$109.0827	$109.08	$109.10	$109.10
7 purchase totals =	$551.43		$591.0703	$591.07	$591.15	$591.00