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	$210.73	10.726%	$233.3329	$233.33	$233.35	$233.30
Purchase #2	$137.35	12.549%	$154.5861	$154.59	$154.60	$154.60
Purchase #3	$250.93	11.620%	$280.0881	$280.09	$280.10	$280.10
Purchase #4	$53.76	10.865%	$59.601	$59.60	$59.60	$59.60
Purchase #5	$146.28	12.125%	$164.0165	$164.02	$164.00	$164.00
Purchase #6	$14.35	5.536%	$15.1444	$15.14	$15.15	$15.10
Purchase #7	$159.53	7.696%	$171.8074	$171.81	$171.80	$171.80
7 purchase totals =	$972.93		$1,078.5764	$1,078.58	$1,078.60	$1,078.50