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	$120.59	10.644%	$133.4256	$133.43	$133.45	$133.40
Purchase #2	$148.86	4.482%	$155.5319	$155.53	$155.55	$155.50
Purchase #3	$20.64	3.439%	$21.3498	$21.35	$21.35	$21.30
Purchase #4	$80.58	12.815%	$90.9063	$90.91	$90.90	$90.90
Purchase #5	$112.46	3.625%	$116.5367	$116.54	$116.55	$116.50
Purchase #6	$19.66	4.716%	$20.5872	$20.59	$20.60	$20.60
Purchase #7	$24.90	9.486%	$27.262	$27.26	$27.25	$27.30
7 purchase totals =	$527.69		$565.5995	$565.61	$565.65	$565.50