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	$103.58	4.526%	$108.268	$108.27	$108.25	$108.30
Purchase #2	$230.79	13.641%	$262.2721	$262.27	$262.25	$262.30
Purchase #3	$82.32	12.274%	$92.424	$92.42	$92.40	$92.40
Purchase #4	$250.75	11.682%	$280.0426	$280.04	$280.05	$280.00
Purchase #5	$59.52	8.550%	$64.609	$64.61	$64.60	$64.60
Purchase #6	$248.32	6.870%	$265.3796	$265.38	$265.40	$265.40
Purchase #7	$152.84	11.339%	$170.1705	$170.17	$170.15	$170.20
7 purchase totals =	$1,128.12		$1,243.1658	$1,243.16	$1,243.10	$1,243.20