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	$237.34	7.671%	$255.5464	$255.55	$255.55	$255.50
Purchase #2	$39.97	8.840%	$43.5033	$43.50	$43.50	$43.50
Purchase #3	$250.60	11.554%	$279.5543	$279.55	$279.55	$279.60
Purchase #4	$60.37	11.631%	$67.3916	$67.39	$67.40	$67.40
Purchase #5	$80.61	12.527%	$90.708	$90.71	$90.70	$90.70
Purchase #6	$102.35	5.472%	$107.9506	$107.95	$107.95	$108.00
Purchase #7	$129.98	3.777%	$134.8893	$134.89	$134.90	$134.90
7 purchase totals =	$901.22		$979.5435	$979.54	$979.55	$979.60