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	$238.27	7.147%	$255.2992	$255.30	$255.30	$255.30
Purchase #2	$86.56	6.389%	$92.0903	$92.09	$92.10	$92.10
Purchase #3	$97.86	7.194%	$104.9	$104.90	$104.90	$104.90
Purchase #4	$152.75	4.491%	$159.61	$159.61	$159.60	$159.60
Purchase #5	$113.63	12.583%	$127.9281	$127.93	$127.95	$127.90
Purchase #6	$33.50	13.210%	$37.9254	$37.93	$37.95	$37.90
Purchase #7	$198.38	7.472%	$213.203	$213.20	$213.20	$213.20
7 purchase totals =	$920.95		$990.9560	$990.96	$991.00	$990.90