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	$20.73	3.429%	$21.4408	$21.44	$21.45	$21.40
Purchase #2	$80.95	3.726%	$83.9662	$83.97	$83.95	$84.00
Purchase #3	$158.86	4.398%	$165.8467	$165.85	$165.85	$165.80
Purchase #4	$14.39	6.729%	$15.3583	$15.36	$15.35	$15.40
Purchase #5	$11.98	9.691%	$13.141	$13.14	$13.15	$13.10
Purchase #6	$33.34	11.174%	$37.0654	$37.07	$37.05	$37.10
Purchase #7	$142.53	13.623%	$161.9469	$161.95	$161.95	$161.90
7 purchase totals =	$462.78		$498.7653	$498.78	$498.75	$498.70