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	$19.39	9.119%	$21.1582	$21.16	$21.15	$21.20
Purchase #2	$112.85	8.459%	$122.396	$122.40	$122.40	$122.40
Purchase #3	$162.59	7.594%	$174.9371	$174.94	$174.95	$174.90
Purchase #4	$38.83	12.611%	$43.7269	$43.73	$43.75	$43.70
Purchase #5	$181.82	7.843%	$196.0801	$196.08	$196.10	$196.10
Purchase #6	$106.60	4.327%	$111.2126	$111.21	$111.20	$111.20
Purchase #7	$104.90	10.371%	$115.7792	$115.78	$115.80	$115.80
7 purchase totals =	$726.98		$785.2901	$785.30	$785.35	$785.30