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	$97.41	6.344%	$103.5897	$103.59	$103.60	$103.60
Purchase #2	$56.45	8.390%	$61.1862	$61.19	$61.20	$61.20
Purchase #3	$132.98	5.205%	$139.9016	$139.90	$139.90	$139.90
Purchase #4	$208.32	12.117%	$233.5621	$233.56	$233.55	$233.60
Purchase #5	$112.41	9.495%	$123.0833	$123.08	$123.10	$123.10
Purchase #6	$228.72	4.287%	$238.5252	$238.53	$238.55	$238.50
Purchase #7	$250.78	8.782%	$272.8035	$272.80	$272.80	$272.80
7 purchase totals =	$1,087.07		$1,172.6516	$1,172.65	$1,172.70	$1,172.70