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	$47.43	13.175%	$53.6789	$53.68	$53.70	$53.70
Purchase #2	$218.62	7.730%	$235.5193	$235.52	$235.50	$235.50
Purchase #3	$142.61	9.694%	$156.4346	$156.43	$156.45	$156.40
Purchase #4	$204.40	10.305%	$225.4634	$225.46	$225.45	$225.50
Purchase #5	$81.54	11.437%	$90.8657	$90.87	$90.85	$90.90
Purchase #6	$44.45	11.143%	$49.4031	$49.40	$49.40	$49.40
Purchase #7	$134.64	7.426%	$144.6384	$144.64	$144.65	$144.60
7 purchase totals =	$873.69		$956.0034	$956.00	$956.00	$956.00