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	$65.39	8.412%	$70.8906	$70.89	$70.90	$70.90
Purchase #2	$230.73	12.287%	$259.0798	$259.08	$259.10	$259.10
Purchase #3	$124.49	5.710%	$131.5984	$131.60	$131.60	$131.60
Purchase #4	$14.94	5.419%	$15.7496	$15.75	$15.75	$15.70
Purchase #5	$73.73	11.744%	$82.3889	$82.39	$82.40	$82.40
Purchase #6	$53.85	4.721%	$56.3923	$56.39	$56.40	$56.40
Purchase #7	$14.40	9.429%	$15.7578	$15.76	$15.75	$15.80
7 purchase totals =	$577.53		$631.8574	$631.86	$631.90	$631.90