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	$38.50	10.284%	$42.4593	$42.46	$42.45	$42.50
Purchase #2	$65.75	4.256%	$68.5483	$68.55	$68.55	$68.50
Purchase #3	$107.43	8.348%	$116.3983	$116.40	$116.40	$116.40
Purchase #4	$98.72	10.510%	$109.0955	$109.10	$109.10	$109.10
Purchase #5	$241.28	6.772%	$257.6195	$257.62	$257.60	$257.60
Purchase #6	$212.72	11.206%	$236.5574	$236.56	$236.55	$236.60
Purchase #7	$248.92	4.613%	$260.4027	$260.40	$260.40	$260.40
7 purchase totals =	$1,013.32		$1,091.0810	$1,091.09	$1,091.05	$1,091.10