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	$187.81	11.782%	$209.9378	$209.94	$209.95	$209.90
Purchase #2	$138.83	8.158%	$150.1558	$150.16	$150.15	$150.20
Purchase #3	$53.38	11.871%	$59.7167	$59.72	$59.70	$59.70
Purchase #4	$176.80	13.390%	$200.4735	$200.47	$200.45	$200.50
Purchase #5	$63.46	11.642%	$70.848	$70.85	$70.85	$70.80
Purchase #6	$103.77	3.190%	$107.0803	$107.08	$107.10	$107.10
Purchase #7	$43.85	3.587%	$45.4229	$45.42	$45.40	$45.40
7 purchase totals =	$767.90		$843.6350	$843.64	$843.60	$843.60