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	$123.62	13.387%	$140.169	$140.17	$140.15	$140.20
Purchase #2	$215.46	9.836%	$236.6526	$236.65	$236.65	$236.70
Purchase #3	$158.35	9.353%	$173.1605	$173.16	$173.15	$173.20
Purchase #4	$112.90	5.661%	$119.2913	$119.29	$119.30	$119.30
Purchase #5	$241.95	6.339%	$257.2872	$257.29	$257.30	$257.30
Purchase #6	$64.32	10.196%	$70.8781	$70.88	$70.90	$70.90
Purchase #7	$78.50	13.581%	$89.1611	$89.16	$89.15	$89.20
7 purchase totals =	$995.10		$1,086.5998	$1,086.60	$1,086.60	$1,086.80