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	$78.29	5.322%	$82.4566	$82.46	$82.45	$82.50
Purchase #2	$123.62	8.245%	$133.8125	$133.81	$133.80	$133.80
Purchase #3	$81.77	10.788%	$90.5913	$90.59	$90.60	$90.60
Purchase #4	$101.46	10.196%	$111.8049	$111.80	$111.80	$111.80
Purchase #5	$130.27	13.732%	$148.1587	$148.16	$148.15	$148.20
Purchase #6	$7.71	9.155%	$8.4159	$8.42	$8.40	$8.40
Purchase #7	$185.65	12.158%	$208.2213	$208.22	$208.20	$208.20
7 purchase totals =	$708.77		$783.4612	$783.46	$783.40	$783.50