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	$34.94	9.721%	$38.3365	$38.34	$38.35	$38.30
Purchase #2	$39.43	7.140%	$42.2453	$42.25	$42.25	$42.20
Purchase #3	$188.60	4.273%	$196.6589	$196.66	$196.65	$196.70
Purchase #4	$142.47	4.242%	$148.5136	$148.51	$148.50	$148.50
Purchase #5	$188.52	10.670%	$208.6351	$208.64	$208.65	$208.60
Purchase #6	$245.71	12.353%	$276.0626	$276.06	$276.05	$276.10
Purchase #7	$116.85	9.818%	$128.3223	$128.32	$128.30	$128.30
7 purchase totals =	$956.52		$1,038.7743	$1,038.78	$1,038.75	$1,038.70