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	$238.99	8.639%	$259.6363	$259.64	$259.65	$259.60
Purchase #2	$192.39	11.697%	$214.8939	$214.89	$214.90	$214.90
Purchase #3	$80.63	3.165%	$83.1819	$83.18	$83.20	$83.20
Purchase #4	$86.87	3.160%	$89.6151	$89.62	$89.60	$89.60
Purchase #5	$38.47	10.187%	$42.3889	$42.39	$42.40	$42.40
Purchase #6	$46.30	5.594%	$48.89	$48.89	$48.90	$48.90
Purchase #7	$34.53	13.860%	$39.3159	$39.32	$39.30	$39.30
7 purchase totals =	$718.18		$777.9220	$777.93	$777.95	$777.90