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	$134.40	3.508%	$139.1148	$139.11	$139.10	$139.10
Purchase #2	$248.94	6.601%	$265.3725	$265.37	$265.35	$265.40
Purchase #3	$244.83	5.631%	$258.6164	$258.62	$258.60	$258.60
Purchase #4	$246.51	13.264%	$279.2071	$279.21	$279.20	$279.20
Purchase #5	$158.91	4.177%	$165.5477	$165.55	$165.55	$165.50
Purchase #6	$137.63	3.119%	$141.9227	$141.92	$141.90	$141.90
Purchase #7	$246.80	13.631%	$280.4413	$280.44	$280.45	$280.40
7 purchase totals =	$1,418.02		$1,530.2225	$1,530.22	$1,530.15	$1,530.10