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	$212.34	13.353%	$240.6938	$240.69	$240.70	$240.70
Purchase #2	$242.80	5.351%	$255.7922	$255.79	$255.80	$255.80
Purchase #3	$129.61	9.756%	$142.2548	$142.25	$142.25	$142.30
Purchase #4	$79.75	13.390%	$90.4285	$90.43	$90.45	$90.40
Purchase #5	$151.48	8.398%	$164.2013	$164.20	$164.20	$164.20
Purchase #6	$190.77	4.168%	$198.7213	$198.72	$198.70	$198.70
Purchase #7	$215.51	8.798%	$234.4706	$234.47	$234.45	$234.50
7 purchase totals =	$1,222.26		$1,326.5625	$1,326.55	$1,326.55	$1,326.60