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	$13.71	6.826%	$14.6458	$14.65	$14.65	$14.60
Purchase #2	$47.25	9.105%	$51.5521	$51.55	$51.55	$51.60
Purchase #3	$166.64	4.185%	$173.6139	$173.61	$173.60	$173.60
Purchase #4	$90.91	5.772%	$96.1573	$96.16	$96.15	$96.20
Purchase #5	$137.58	7.836%	$148.3608	$148.36	$148.35	$148.40
Purchase #6	$108.26	3.258%	$111.7871	$111.79	$111.80	$111.80
Purchase #7	$232.87	3.844%	$241.8215	$241.82	$241.80	$241.80
7 purchase totals =	$797.22		$837.9385	$837.94	$837.90	$838.00