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	$57.78	9.215%	$63.1044	$63.10	$63.10	$63.10
Purchase #2	$211.61	4.307%	$220.724	$220.72	$220.70	$220.70
Purchase #3	$222.96	11.314%	$248.1857	$248.19	$248.20	$248.20
Purchase #4	$244.51	4.721%	$256.0533	$256.05	$256.05	$256.10
Purchase #5	$62.34	7.254%	$66.8621	$66.86	$66.85	$66.90
Purchase #6	$13.39	10.744%	$14.8286	$14.83	$14.85	$14.80
Purchase #7	$205.35	12.283%	$230.5731	$230.57	$230.55	$230.60
7 purchase totals =	$1,017.94		$1,100.3312	$1,100.32	$1,100.30	$1,100.40