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	$16.39	6.513%	$17.4575	$17.46	$17.45	$17.50
Purchase #2	$145.87	8.527%	$158.3083	$158.31	$158.30	$158.30
Purchase #3	$100.26	5.322%	$105.5958	$105.60	$105.60	$105.60
Purchase #4	$135.38	12.208%	$151.9072	$151.91	$151.90	$151.90
Purchase #5	$224.45	9.112%	$244.9019	$244.90	$244.90	$244.90
Purchase #6	$99.94	11.448%	$111.3811	$111.38	$111.40	$111.40
Purchase #7	$246.94	10.669%	$273.286	$273.29	$273.30	$273.30
7 purchase totals =	$969.23		$1,062.8378	$1,062.85	$1,062.85	$1,062.90