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	$36.26	3.420%	$37.5001	$37.50	$37.50	$37.50
Purchase #2	$153.61	12.749%	$173.1937	$173.19	$173.20	$173.20
Purchase #3	$27.71	13.436%	$31.4331	$31.43	$31.45	$31.40
Purchase #4	$125.60	9.614%	$137.6752	$137.68	$137.70	$137.70
Purchase #5	$130.32	3.271%	$134.5828	$134.58	$134.60	$134.60
Purchase #6	$115.49	10.269%	$127.3497	$127.35	$127.35	$127.30
Purchase #7	$114.94	7.377%	$123.4191	$123.42	$123.40	$123.40
7 purchase totals =	$703.93		$765.1537	$765.15	$765.20	$765.10