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	$20.88	4.294%	$21.7766	$21.78	$21.80	$21.80
Purchase #2	$248.91	12.828%	$280.8402	$280.84	$280.85	$280.80
Purchase #3	$107.45	12.252%	$120.6148	$120.61	$120.60	$120.60
Purchase #4	$51.30	3.196%	$52.9395	$52.94	$52.95	$52.90
Purchase #5	$99.88	9.597%	$109.4655	$109.47	$109.45	$109.50
Purchase #6	$14.55	8.397%	$15.7718	$15.77	$15.75	$15.80
Purchase #7	$11.58	5.569%	$12.2249	$12.22	$12.20	$12.20
7 purchase totals =	$554.55		$613.6333	$613.63	$613.60	$613.60