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	$20.81	12.738%	$23.4608	$23.46	$23.45	$23.50
Purchase #2	$13.79	6.560%	$14.6946	$14.69	$14.70	$14.70
Purchase #3	$249.46	11.243%	$277.5068	$277.51	$277.50	$277.50
Purchase #4	$150.69	9.450%	$164.9302	$164.93	$164.95	$164.90
Purchase #5	$115.53	11.461%	$128.7709	$128.77	$128.75	$128.80
Purchase #6	$52.59	3.309%	$54.3302	$54.33	$54.35	$54.30
Purchase #7	$172.36	7.521%	$185.3232	$185.32	$185.30	$185.30
7 purchase totals =	$775.23		$849.0167	$849.01	$849.00	$849.00