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	$84.43	5.522%	$89.0922	$89.09	$89.10	$89.10
Purchase #2	$140.81	11.272%	$156.6821	$156.68	$156.70	$156.70
Purchase #3	$226.89	3.811%	$235.5368	$235.54	$235.55	$235.50
Purchase #4	$32.30	11.259%	$35.9367	$35.94	$35.95	$35.90
Purchase #5	$13.98	13.226%	$15.829	$15.83	$15.85	$15.80
Purchase #6	$17.52	5.139%	$18.4204	$18.42	$18.40	$18.40
Purchase #7	$5.52	13.764%	$6.2798	$6.28	$6.30	$6.30
7 purchase totals =	$521.45		$557.7770	$557.78	$557.85	$557.70