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	$244.31	6.346%	$259.8139	$259.81	$259.80	$259.80
Purchase #2	$52.59	13.351%	$59.6113	$59.61	$59.60	$59.60
Purchase #3	$148.68	12.659%	$167.5014	$167.50	$167.50	$167.50
Purchase #4	$246.37	4.852%	$258.3239	$258.32	$258.30	$258.30
Purchase #5	$111.60	4.116%	$116.1935	$116.19	$116.20	$116.20
Purchase #6	$153.85	13.778%	$175.0475	$175.05	$175.05	$175.00
Purchase #7	$228.51	13.335%	$258.9818	$258.98	$259.00	$259.00
7 purchase totals =	$1,185.91		$1,295.4733	$1,295.46	$1,295.45	$1,295.40