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	$14.88	4.307%	$15.5209	$15.52	$15.50	$15.50
Purchase #2	$153.89	3.272%	$158.9253	$158.93	$158.95	$158.90
Purchase #3	$56.84	5.641%	$60.0463	$60.05	$60.05	$60.00
Purchase #4	$230.65	3.194%	$238.017	$238.02	$238.00	$238.00
Purchase #5	$120.31	5.476%	$126.8982	$126.90	$126.90	$126.90
Purchase #6	$88.89	11.144%	$98.7959	$98.80	$98.80	$98.80
Purchase #7	$78.88	8.715%	$85.7544	$85.75	$85.75	$85.80
7 purchase totals =	$744.34		$783.9580	$783.97	$783.95	$783.90