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	$100.28	11.207%	$111.5184	$111.52	$111.50	$111.50
Purchase #2	$121.25	9.412%	$132.6621	$132.66	$132.65	$132.70
Purchase #3	$41.68	13.847%	$47.4514	$47.45	$47.45	$47.50
Purchase #4	$100.34	4.158%	$104.5121	$104.51	$104.50	$104.50
Purchase #5	$58.61	11.443%	$65.3167	$65.32	$65.30	$65.30
Purchase #6	$107.75	8.322%	$116.717	$116.72	$116.70	$116.70
Purchase #7	$190.25	11.126%	$211.4172	$211.42	$211.40	$211.40
7 purchase totals =	$720.16		$789.5949	$789.60	$789.50	$789.60