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	$48.66	4.236%	$50.7212	$50.72	$50.70	$50.70
Purchase #2	$98.45	12.874%	$111.1245	$111.12	$111.10	$111.10
Purchase #3	$77.26	12.711%	$87.0805	$87.08	$87.10	$87.10
Purchase #4	$97.63	13.738%	$111.0424	$111.04	$111.05	$111.00
Purchase #5	$12.69	13.203%	$14.3655	$14.37	$14.35	$14.40
Purchase #6	$33.95	4.850%	$35.5966	$35.60	$35.60	$35.60
Purchase #7	$175.55	8.811%	$191.0177	$191.02	$191.00	$191.00
7 purchase totals =	$544.19		$600.9484	$600.95	$600.90	$600.90