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	$18.82	13.608%	$21.381	$21.38	$21.40	$21.40
Purchase #2	$39.40	10.518%	$43.5441	$43.54	$43.55	$43.50
Purchase #3	$200.68	13.778%	$228.3297	$228.33	$228.35	$228.30
Purchase #4	$127.61	4.703%	$133.6115	$133.61	$133.60	$133.60
Purchase #5	$142.51	8.529%	$154.6647	$154.66	$154.65	$154.70
Purchase #6	$157.53	6.357%	$167.5442	$167.54	$167.55	$167.50
Purchase #7	$109.79	10.652%	$121.4848	$121.48	$121.50	$121.50
7 purchase totals =	$796.34		$870.5600	$870.54	$870.60	$870.50