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	$45.49	11.206%	$50.5876	$50.59	$50.60	$50.60
Purchase #2	$123.61	7.455%	$132.8251	$132.83	$132.85	$132.80
Purchase #3	$97.95	7.203%	$105.0053	$105.01	$105.00	$105.00
Purchase #4	$184.68	13.411%	$209.4474	$209.45	$209.45	$209.40
Purchase #5	$122.62	4.250%	$127.8314	$127.83	$127.85	$127.80
Purchase #6	$68.47	6.529%	$72.9404	$72.94	$72.95	$72.90
Purchase #7	$37.95	3.635%	$39.3295	$39.33	$39.35	$39.30
7 purchase totals =	$680.77		$737.9667	$737.98	$738.05	$737.80