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	$35.72	11.660%	$39.885	$39.89	$39.90	$39.90
Purchase #2	$15.89	4.810%	$16.6543	$16.65	$16.65	$16.70
Purchase #3	$167.38	12.846%	$188.8816	$188.88	$188.90	$188.90
Purchase #4	$184.37	13.429%	$209.129	$209.13	$209.15	$209.10
Purchase #5	$126.51	12.807%	$142.7121	$142.71	$142.70	$142.70
Purchase #6	$111.40	6.713%	$118.8783	$118.88	$118.90	$118.90
Purchase #7	$138.92	12.476%	$156.2517	$156.25	$156.25	$156.30
7 purchase totals =	$780.19		$872.3920	$872.39	$872.45	$872.50