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	$108.65	13.769%	$123.61	$123.61	$123.60	$123.60
Purchase #2	$19.72	11.833%	$22.0535	$22.05	$22.05	$22.10
Purchase #3	$138.65	5.862%	$146.7777	$146.78	$146.80	$146.80
Purchase #4	$56.79	3.596%	$58.8322	$58.83	$58.85	$58.80
Purchase #5	$20.57	5.724%	$21.7474	$21.75	$21.75	$21.70
Purchase #6	$137.40	13.577%	$156.0548	$156.05	$156.05	$156.10
Purchase #7	$67.95	3.696%	$70.4614	$70.46	$70.45	$70.50
7 purchase totals =	$549.73		$599.5370	$599.53	$599.55	$599.60