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	$158.77	8.529%	$172.3115	$172.31	$172.30	$172.30
Purchase #2	$62.95	12.599%	$70.8811	$70.88	$70.90	$70.90
Purchase #3	$131.52	10.242%	$144.9903	$144.99	$145.00	$145.00
Purchase #4	$70.58	11.693%	$78.8329	$78.83	$78.85	$78.80
Purchase #5	$7.25	9.255%	$7.921	$7.92	$7.90	$7.90
Purchase #6	$176.45	5.607%	$186.3436	$186.34	$186.35	$186.30
Purchase #7	$109.42	4.111%	$113.9183	$113.92	$113.90	$113.90
7 purchase totals =	$716.94		$775.1987	$775.19	$775.20	$775.10