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	$132.34	12.194%	$148.4775	$148.48	$148.50	$148.50
Purchase #2	$162.54	4.260%	$169.4642	$169.46	$169.45	$169.50
Purchase #3	$14.62	3.116%	$15.0756	$15.08	$15.10	$15.10
Purchase #4	$117.83	8.402%	$127.7301	$127.73	$127.75	$127.70
Purchase #5	$70.27	13.642%	$79.8562	$79.86	$79.85	$79.90
Purchase #6	$108.31	11.150%	$120.3866	$120.39	$120.40	$120.40
Purchase #7	$18.71	4.153%	$19.487	$19.49	$19.50	$19.50
7 purchase totals =	$624.62		$680.4772	$680.49	$680.55	$680.60