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	$95.51	4.241%	$99.5606	$99.56	$99.55	$99.60
Purchase #2	$177.51	4.553%	$185.592	$185.59	$185.60	$185.60
Purchase #3	$97.48	9.202%	$106.4501	$106.45	$106.45	$106.50
Purchase #4	$132.53	9.343%	$144.9123	$144.91	$144.90	$144.90
Purchase #5	$164.65	4.339%	$171.7942	$171.79	$171.80	$171.80
Purchase #6	$21.64	5.859%	$22.9079	$22.91	$22.90	$22.90
Purchase #7	$152.90	3.239%	$157.8524	$157.85	$157.85	$157.90
7 purchase totals =	$842.22		$889.0695	$889.06	$889.05	$889.20