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	$214.29	5.867%	$226.8624	$226.86	$226.85	$226.90
Purchase #2	$242.82	11.843%	$271.5772	$271.58	$271.60	$271.60
Purchase #3	$239.53	12.712%	$269.9791	$269.98	$270.00	$270.00
Purchase #4	$138.31	10.182%	$152.3927	$152.39	$152.40	$152.40
Purchase #5	$35.70	4.856%	$37.4336	$37.43	$37.45	$37.40
Purchase #6	$182.29	13.452%	$206.8117	$206.81	$206.80	$206.80
Purchase #7	$132.43	8.634%	$143.864	$143.86	$143.85	$143.90
7 purchase totals =	$1,185.37		$1,308.9207	$1,308.91	$1,308.95	$1,309.00