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	$158.78	13.678%	$180.4979	$180.50	$180.50	$180.50
Purchase #2	$146.67	4.622%	$153.4491	$153.45	$153.45	$153.40
Purchase #3	$245.46	6.143%	$260.5386	$260.54	$260.55	$260.50
Purchase #4	$80.70	12.418%	$90.7213	$90.72	$90.70	$90.70
Purchase #5	$169.77	4.346%	$177.1482	$177.15	$177.15	$177.10
Purchase #6	$82.66	4.710%	$86.5533	$86.55	$86.55	$86.60
Purchase #7	$168.42	11.406%	$187.63	$187.63	$187.65	$187.60
7 purchase totals =	$1,052.46		$1,136.5384	$1,136.54	$1,136.55	$1,136.40