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	$238.69	11.358%	$265.8004	$265.80	$265.80	$265.80
Purchase #2	$80.81	12.477%	$90.8927	$90.89	$90.90	$90.90
Purchase #3	$137.25	4.497%	$143.4221	$143.42	$143.40	$143.40
Purchase #4	$140.30	12.562%	$157.9245	$157.92	$157.90	$157.90
Purchase #5	$242.44	4.617%	$253.6335	$253.63	$253.65	$253.60
Purchase #6	$81.55	10.671%	$90.2522	$90.25	$90.25	$90.30
Purchase #7	$43.91	13.664%	$49.9099	$49.91	$49.90	$49.90
7 purchase totals =	$964.95		$1,051.8353	$1,051.82	$1,051.80	$1,051.80