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	$200.74	10.542%	$221.902	$221.90	$221.90	$221.90
Purchase #2	$157.40	7.224%	$168.7706	$168.77	$168.75	$168.80
Purchase #3	$88.56	10.122%	$97.524	$97.52	$97.50	$97.50
Purchase #4	$217.85	7.128%	$233.3783	$233.38	$233.40	$233.40
Purchase #5	$110.46	11.726%	$123.4125	$123.41	$123.40	$123.40
Purchase #6	$11.78	12.582%	$13.2622	$13.26	$13.25	$13.30
Purchase #7	$111.65	13.382%	$126.591	$126.59	$126.60	$126.60
7 purchase totals =	$898.44		$984.8406	$984.83	$984.80	$984.90