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	$134.54	3.530%	$139.2893	$139.29	$139.30	$139.30
Purchase #2	$101.58	6.832%	$108.5199	$108.52	$108.50	$108.50
Purchase #3	$44.48	9.605%	$48.7523	$48.75	$48.75	$48.80
Purchase #4	$241.49	13.291%	$273.5864	$273.59	$273.60	$273.60
Purchase #5	$209.79	13.663%	$238.4536	$238.45	$238.45	$238.50
Purchase #6	$178.40	13.695%	$202.8319	$202.83	$202.85	$202.80
Purchase #7	$142.72	12.534%	$160.6085	$160.61	$160.60	$160.60
7 purchase totals =	$1,053.00		$1,172.0419	$1,172.04	$1,172.05	$1,172.10