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	$134.75	6.755%	$143.8524	$143.85	$143.85	$143.90
Purchase #2	$145.26	7.840%	$156.6484	$156.65	$156.65	$156.60
Purchase #3	$139.35	13.633%	$158.3476	$158.35	$158.35	$158.30
Purchase #4	$41.60	3.139%	$42.9058	$42.91	$42.90	$42.90
Purchase #5	$29.64	4.269%	$30.9053	$30.91	$30.90	$30.90
Purchase #6	$49.54	12.553%	$55.7588	$55.76	$55.75	$55.80
Purchase #7	$40.49	7.643%	$43.5847	$43.58	$43.60	$43.60
7 purchase totals =	$580.63		$632.0030	$632.01	$632.00	$632.00