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	$68.84	5.608%	$72.7005	$72.70	$72.70	$72.70
Purchase #2	$139.87	5.341%	$147.3405	$147.34	$147.35	$147.30
Purchase #3	$126.25	4.446%	$131.8631	$131.86	$131.85	$131.90
Purchase #4	$117.51	8.343%	$127.3139	$127.31	$127.30	$127.30
Purchase #5	$12.88	9.287%	$14.0762	$14.08	$14.10	$14.10
Purchase #6	$14.36	3.314%	$14.8359	$14.84	$14.85	$14.80
Purchase #7	$53.92	5.372%	$56.8166	$56.82	$56.80	$56.80
7 purchase totals =	$533.63		$564.9467	$564.95	$564.95	$564.90