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	$19.78	10.705%	$21.8974	$21.90	$21.90	$21.90
Purchase #2	$62.77	13.785%	$71.4228	$71.42	$71.40	$71.40
Purchase #3	$41.86	9.771%	$45.9501	$45.95	$45.95	$46.00
Purchase #4	$246.92	5.766%	$261.1574	$261.16	$261.15	$261.20
Purchase #5	$117.43	9.328%	$128.3839	$128.38	$128.40	$128.40
Purchase #6	$68.31	3.690%	$70.8306	$70.83	$70.85	$70.80
Purchase #7	$131.39	10.222%	$144.8207	$144.82	$144.80	$144.80
7 purchase totals =	$688.46		$744.4629	$744.46	$744.45	$744.50