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	$249.62	12.312%	$280.3532	$280.35	$280.35	$280.40
Purchase #2	$220.55	12.704%	$248.5687	$248.57	$248.55	$248.60
Purchase #3	$160.80	7.771%	$173.2958	$173.30	$173.30	$173.30
Purchase #4	$157.40	10.264%	$173.5555	$173.56	$173.55	$173.60
Purchase #5	$64.77	11.540%	$72.2445	$72.24	$72.25	$72.20
Purchase #6	$134.46	7.443%	$144.4679	$144.47	$144.45	$144.50
Purchase #7	$56.51	10.785%	$62.6046	$62.60	$62.60	$62.60
7 purchase totals =	$1,044.11		$1,155.0902	$1,155.09	$1,155.05	$1,155.20