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	$241.83	11.446%	$269.5099	$269.51	$269.50	$269.50
Purchase #2	$103.91	7.796%	$112.0108	$112.01	$112.00	$112.00
Purchase #3	$102.83	5.239%	$108.2173	$108.22	$108.20	$108.20
Purchase #4	$141.72	11.819%	$158.4699	$158.47	$158.45	$158.50
Purchase #5	$32.31	9.162%	$35.2702	$35.27	$35.25	$35.30
Purchase #6	$18.27	6.502%	$19.4579	$19.46	$19.45	$19.50
Purchase #7	$189.27	5.871%	$200.382	$200.38	$200.40	$200.40
7 purchase totals =	$830.14		$903.3180	$903.32	$903.25	$903.40