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	$94.90	8.788%	$103.2398	$103.24	$103.25	$103.20
Purchase #2	$104.70	6.711%	$111.7264	$111.73	$111.75	$111.70
Purchase #3	$79.61	7.667%	$85.7137	$85.71	$85.70	$85.70
Purchase #4	$205.62	6.638%	$219.2691	$219.27	$219.25	$219.30
Purchase #5	$38.83	11.816%	$43.4182	$43.42	$43.40	$43.40
Purchase #6	$40.35	11.750%	$45.0911	$45.09	$45.10	$45.10
Purchase #7	$26.86	10.168%	$29.5911	$29.59	$29.60	$29.60
7 purchase totals =	$590.87		$638.0494	$638.05	$638.05	$638.00