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	$71.88	3.710%	$74.5467	$74.55	$74.55	$74.50
Purchase #2	$81.84	7.296%	$87.811	$87.81	$87.80	$87.80
Purchase #3	$95.90	4.690%	$100.3977	$100.40	$100.40	$100.40
Purchase #4	$226.66	5.205%	$238.4577	$238.46	$238.45	$238.50
Purchase #5	$102.96	9.253%	$112.4869	$112.49	$112.50	$112.50
Purchase #6	$31.32	10.203%	$34.5156	$34.52	$34.50	$34.50
Purchase #7	$166.83	3.214%	$172.1919	$172.19	$172.20	$172.20
7 purchase totals =	$777.39		$820.4075	$820.42	$820.40	$820.40