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	$165.60	12.403%	$186.1394	$186.14	$186.15	$186.10
Purchase #2	$141.43	9.688%	$155.1317	$155.13	$155.15	$155.10
Purchase #3	$193.70	11.420%	$215.8205	$215.82	$215.80	$215.80
Purchase #4	$238.86	9.412%	$261.3415	$261.34	$261.35	$261.30
Purchase #5	$107.40	3.607%	$111.2739	$111.27	$111.25	$111.30
Purchase #6	$188.47	8.523%	$204.5333	$204.53	$204.55	$204.50
Purchase #7	$169.49	7.141%	$181.5933	$181.59	$181.60	$181.60
7 purchase totals =	$1,204.95		$1,315.8336	$1,315.82	$1,315.85	$1,315.70