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	$20.44	3.403%	$21.1356	$21.14	$21.15	$21.10
Purchase #2	$208.60	6.796%	$222.7765	$222.78	$222.80	$222.80
Purchase #3	$102.40	13.675%	$116.4032	$116.40	$116.40	$116.40
Purchase #4	$40.59	5.796%	$42.9426	$42.94	$42.95	$42.90
Purchase #5	$240.87	8.685%	$261.7896	$261.79	$261.80	$261.80
Purchase #6	$131.43	7.386%	$141.1374	$141.14	$141.15	$141.10
Purchase #7	$166.97	12.243%	$187.4121	$187.41	$187.40	$187.40
7 purchase totals =	$911.30		$993.5970	$993.60	$993.65	$993.50