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	$156.55	6.179%	$166.2232	$166.22	$166.20	$166.20
Purchase #2	$228.57	12.844%	$257.9275	$257.93	$257.95	$257.90
Purchase #3	$178.97	9.860%	$196.6164	$196.62	$196.60	$196.60
Purchase #4	$171.59	11.798%	$191.8342	$191.83	$191.85	$191.80
Purchase #5	$7.97	13.553%	$9.0502	$9.05	$9.05	$9.10
Purchase #6	$219.74	5.353%	$231.5027	$231.50	$231.50	$231.50
Purchase #7	$82.39	10.285%	$90.8638	$90.86	$90.85	$90.90
7 purchase totals =	$1,045.78		$1,144.0180	$1,144.01	$1,144.00	$1,144.00