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	$224.42	13.219%	$254.0861	$254.09	$254.10	$254.10
Purchase #2	$118.78	5.182%	$124.9352	$124.94	$124.95	$124.90
Purchase #3	$127.26	11.815%	$142.2958	$142.30	$142.30	$142.30
Purchase #4	$123.86	6.495%	$131.9047	$131.90	$131.90	$131.90
Purchase #5	$65.59	13.577%	$74.4952	$74.50	$74.50	$74.50
Purchase #6	$202.55	12.520%	$227.9093	$227.91	$227.90	$227.90
Purchase #7	$34.94	7.242%	$37.4704	$37.47	$37.45	$37.50
7 purchase totals =	$897.40		$993.0967	$993.11	$993.10	$993.10