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	$235.27	8.223%	$254.6163	$254.62	$254.60	$254.60
Purchase #2	$136.70	4.483%	$142.8283	$142.83	$142.85	$142.80
Purchase #3	$44.63	9.417%	$48.8328	$48.83	$48.85	$48.80
Purchase #4	$174.40	13.844%	$198.5439	$198.54	$198.55	$198.50
Purchase #5	$95.77	8.196%	$103.6193	$103.62	$103.60	$103.60
Purchase #6	$44.78	11.258%	$49.8213	$49.82	$49.80	$49.80
Purchase #7	$112.33	4.669%	$117.5747	$117.57	$117.55	$117.60
7 purchase totals =	$843.88		$915.8366	$915.83	$915.80	$915.70