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	$89.81	11.745%	$100.3582	$100.36	$100.35	$100.40
Purchase #2	$132.81	5.815%	$140.5329	$140.53	$140.55	$140.50
Purchase #3	$107.32	5.721%	$113.4598	$113.46	$113.45	$113.50
Purchase #4	$156.62	7.321%	$168.0862	$168.09	$168.10	$168.10
Purchase #5	$14.59	4.530%	$15.2509	$15.25	$15.25	$15.30
Purchase #6	$74.40	12.828%	$83.944	$83.94	$83.95	$83.90
Purchase #7	$85.90	10.470%	$94.8937	$94.89	$94.90	$94.90
7 purchase totals =	$661.45		$716.5257	$716.52	$716.55	$716.60