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	$40.86	9.125%	$44.5885	$44.59	$44.60	$44.60
Purchase #2	$224.52	13.106%	$253.9456	$253.95	$253.95	$253.90
Purchase #3	$75.70	6.484%	$80.6084	$80.61	$80.60	$80.60
Purchase #4	$40.37	4.393%	$42.1435	$42.14	$42.15	$42.10
Purchase #5	$49.69	9.814%	$54.5666	$54.57	$54.55	$54.60
Purchase #6	$168.40	12.832%	$190.0091	$190.01	$190.00	$190.00
Purchase #7	$208.34	10.672%	$230.574	$230.57	$230.55	$230.60
7 purchase totals =	$807.88		$896.4357	$896.44	$896.40	$896.40