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	$145.74	13.320%	$165.1526	$165.15	$165.15	$165.20
Purchase #2	$48.68	13.441%	$55.2231	$55.22	$55.20	$55.20
Purchase #3	$167.67	3.545%	$173.6139	$173.61	$173.60	$173.60
Purchase #4	$181.30	3.218%	$187.1342	$187.13	$187.15	$187.10
Purchase #5	$82.77	11.664%	$92.4243	$92.42	$92.40	$92.40
Purchase #6	$38.87	12.557%	$43.7509	$43.75	$43.75	$43.80
Purchase #7	$181.35	13.388%	$205.6291	$205.63	$205.65	$205.60
7 purchase totals =	$846.38		$922.9281	$922.91	$922.90	$922.90