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	$35.69	11.177%	$39.6791	$39.68	$39.70	$39.70
Purchase #2	$160.53	5.672%	$169.6353	$169.64	$169.65	$169.60
Purchase #3	$179.60	3.361%	$185.6364	$185.64	$185.65	$185.60
Purchase #4	$178.40	12.116%	$200.0149	$200.01	$200.00	$200.00
Purchase #5	$206.27	3.533%	$213.5575	$213.56	$213.55	$213.60
Purchase #6	$90.62	10.471%	$100.1088	$100.11	$100.10	$100.10
Purchase #7	$46.48	9.295%	$50.8003	$50.80	$50.80	$50.80
7 purchase totals =	$897.59		$959.4323	$959.44	$959.45	$959.40