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	$20.48	4.463%	$21.394	$21.39	$21.40	$21.40
Purchase #2	$247.77	9.391%	$271.0381	$271.04	$271.05	$271.00
Purchase #3	$238.78	11.515%	$266.2755	$266.28	$266.30	$266.30
Purchase #4	$125.77	4.692%	$131.6711	$131.67	$131.65	$131.70
Purchase #5	$33.82	5.798%	$35.7809	$35.78	$35.80	$35.80
Purchase #6	$153.48	10.720%	$169.9331	$169.93	$169.95	$169.90
Purchase #7	$29.51	11.337%	$32.8555	$32.86	$32.85	$32.90
7 purchase totals =	$849.61		$928.9482	$928.95	$929.00	$929.00