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	$6.38	13.169%	$7.2202	$7.22	$7.20	$7.20
Purchase #2	$133.40	7.258%	$143.0822	$143.08	$143.10	$143.10
Purchase #3	$210.86	11.741%	$235.6171	$235.62	$235.60	$235.60
Purchase #4	$160.90	4.703%	$168.4671	$168.47	$168.45	$168.50
Purchase #5	$146.69	10.803%	$162.5369	$162.54	$162.55	$162.50
Purchase #6	$131.41	12.348%	$147.6365	$147.64	$147.65	$147.60
Purchase #7	$124.30	8.223%	$134.5212	$134.52	$134.50	$134.50
7 purchase totals =	$913.94		$999.0812	$999.09	$999.05	$999.00