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	$125.83	8.806%	$136.9106	$136.91	$136.90	$136.90
Purchase #2	$100.78	10.773%	$111.637	$111.64	$111.65	$111.60
Purchase #3	$132.38	7.783%	$142.6831	$142.68	$142.70	$142.70
Purchase #4	$153.66	5.552%	$162.1912	$162.19	$162.20	$162.20
Purchase #5	$250.59	10.714%	$277.4382	$277.44	$277.45	$277.40
Purchase #6	$248.47	5.283%	$261.5967	$261.60	$261.60	$261.60
Purchase #7	$228.36	11.837%	$255.391	$255.39	$255.40	$255.40
7 purchase totals =	$1,240.07		$1,347.8478	$1,347.85	$1,347.90	$1,347.80