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	$138.31	3.400%	$143.0125	$143.01	$143.00	$143.00
Purchase #2	$215.72	12.104%	$241.8307	$241.83	$241.85	$241.80
Purchase #3	$179.77	7.841%	$193.8658	$193.87	$193.85	$193.90
Purchase #4	$209.53	10.645%	$231.8345	$231.83	$231.85	$231.80
Purchase #5	$97.72	6.283%	$103.8597	$103.86	$103.85	$103.90
Purchase #6	$144.50	6.351%	$153.6772	$153.68	$153.70	$153.70
Purchase #7	$38.84	9.785%	$42.6405	$42.64	$42.65	$42.60
7 purchase totals =	$1,024.39		$1,110.7209	$1,110.72	$1,110.75	$1,110.70