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	$136.79	5.594%	$144.442	$144.44	$144.45	$144.40
Purchase #2	$125.97	4.847%	$132.0758	$132.08	$132.10	$132.10
Purchase #3	$34.80	11.529%	$38.8121	$38.81	$38.80	$38.80
Purchase #4	$70.97	10.229%	$78.2295	$78.23	$78.25	$78.20
Purchase #5	$164.92	12.462%	$185.4723	$185.47	$185.45	$185.50
Purchase #6	$77.96	5.613%	$82.3359	$82.34	$82.35	$82.30
Purchase #7	$45.50	11.167%	$50.581	$50.58	$50.60	$50.60
7 purchase totals =	$656.91		$711.9486	$711.95	$712.00	$711.90