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	$9.52	11.715%	$10.6353	$10.64	$10.65	$10.60
Purchase #2	$241.26	12.694%	$271.8855	$271.89	$271.90	$271.90
Purchase #3	$38.98	12.229%	$43.7469	$43.75	$43.75	$43.70
Purchase #4	$93.97	12.590%	$105.8008	$105.80	$105.80	$105.80
Purchase #5	$176.80	11.344%	$196.8562	$196.86	$196.85	$196.90
Purchase #6	$159.32	12.617%	$179.4214	$179.42	$179.40	$179.40
Purchase #7	$7.72	12.825%	$8.7101	$8.71	$8.70	$8.70
7 purchase totals =	$727.57		$817.0562	$817.07	$817.05	$817.00