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	$19.77	3.259%	$20.4143	$20.41	$20.40	$20.40
Purchase #2	$40.42	7.712%	$43.5372	$43.54	$43.55	$43.50
Purchase #3	$28.72	10.144%	$31.6334	$31.63	$31.65	$31.60
Purchase #4	$41.61	11.541%	$46.4122	$46.41	$46.40	$46.40
Purchase #5	$173.38	6.734%	$185.0554	$185.06	$185.05	$185.10
Purchase #6	$131.91	5.262%	$138.8511	$138.85	$138.85	$138.90
Purchase #7	$103.62	8.545%	$112.4743	$112.47	$112.45	$112.50
7 purchase totals =	$539.43		$578.3779	$578.37	$578.35	$578.40