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	$215.45	4.158%	$224.4084	$224.41	$224.40	$224.40
Purchase #2	$197.72	5.464%	$208.5234	$208.52	$208.50	$208.50
Purchase #3	$24.72	9.439%	$27.0533	$27.05	$27.05	$27.10
Purchase #4	$247.60	5.674%	$261.6488	$261.65	$261.65	$261.60
Purchase #5	$19.36	9.767%	$21.2509	$21.25	$21.25	$21.30
Purchase #6	$103.53	8.106%	$111.9221	$111.92	$111.90	$111.90
Purchase #7	$45.63	6.484%	$48.5886	$48.59	$48.60	$48.60
7 purchase totals =	$854.01		$903.3955	$903.39	$903.35	$903.40