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	$248.31	4.602%	$259.7372	$259.74	$259.75	$259.70
Purchase #2	$95.63	11.834%	$106.9469	$106.95	$106.95	$106.90
Purchase #3	$126.81	3.393%	$131.1127	$131.11	$131.10	$131.10
Purchase #4	$165.95	13.640%	$188.5856	$188.59	$188.60	$188.60
Purchase #5	$22.59	13.419%	$25.6214	$25.62	$25.60	$25.60
Purchase #6	$13.52	8.149%	$14.6217	$14.62	$14.60	$14.60
Purchase #7	$105.50	10.467%	$116.5427	$116.54	$116.55	$116.50
7 purchase totals =	$778.31		$843.1682	$843.17	$843.15	$843.00