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	$242.76	6.559%	$258.6826	$258.68	$258.70	$258.70
Purchase #2	$113.88	12.744%	$128.3929	$128.39	$128.40	$128.40
Purchase #3	$126.60	6.136%	$134.3682	$134.37	$134.35	$134.40
Purchase #4	$19.83	3.496%	$20.5233	$20.52	$20.50	$20.50
Purchase #5	$200.99	11.641%	$224.3872	$224.39	$224.40	$224.40
Purchase #6	$61.56	5.145%	$64.7273	$64.73	$64.75	$64.70
Purchase #7	$102.72	8.493%	$111.444	$111.44	$111.45	$111.40
7 purchase totals =	$868.34		$942.5255	$942.52	$942.55	$942.50