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	$112.41	6.565%	$119.7897	$119.79	$119.80	$119.80
Purchase #2	$96.90	6.386%	$103.088	$103.09	$103.10	$103.10
Purchase #3	$137.38	5.426%	$144.8342	$144.83	$144.85	$144.80
Purchase #4	$48.56	12.434%	$54.598	$54.60	$54.60	$54.60
Purchase #5	$224.43	10.411%	$247.7954	$247.80	$247.80	$247.80
Purchase #6	$115.34	3.535%	$119.4173	$119.42	$119.40	$119.40
Purchase #7	$60.47	9.821%	$66.4088	$66.41	$66.40	$66.40
7 purchase totals =	$795.49		$855.9314	$855.94	$855.95	$855.90