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	$24.31	13.644%	$27.6269	$27.63	$27.65	$27.60
Purchase #2	$113.81	11.427%	$126.8151	$126.82	$126.80	$126.80
Purchase #3	$235.40	8.526%	$255.4702	$255.47	$255.45	$255.50
Purchase #4	$162.35	5.637%	$171.5017	$171.50	$171.50	$171.50
Purchase #5	$164.81	13.497%	$187.0544	$187.05	$187.05	$187.10
Purchase #6	$160.92	5.384%	$169.5839	$169.58	$169.60	$169.60
Purchase #7	$187.47	9.354%	$205.0059	$205.01	$205.00	$205.00
7 purchase totals =	$1,049.07		$1,143.0581	$1,143.06	$1,143.05	$1,143.10