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	$234.28	9.481%	$256.4921	$256.49	$256.50	$256.50
Purchase #2	$82.43	5.738%	$87.1598	$87.16	$87.15	$87.20
Purchase #3	$172.52	3.522%	$178.5962	$178.60	$178.60	$178.60
Purchase #4	$226.62	13.371%	$256.9214	$256.92	$256.90	$256.90
Purchase #5	$195.86	13.516%	$222.3324	$222.33	$222.35	$222.30
Purchase #6	$49.53	13.132%	$56.0343	$56.03	$56.05	$56.00
Purchase #7	$80.79	8.144%	$87.3695	$87.37	$87.35	$87.40
7 purchase totals =	$1,042.03		$1,144.9057	$1,144.90	$1,144.90	$1,144.90