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	$38.99	10.376%	$43.0356	$43.04	$43.05	$43.00
Purchase #2	$129.88	12.846%	$146.5644	$146.56	$146.55	$146.60
Purchase #3	$196.40	13.498%	$222.9101	$222.91	$222.90	$222.90
Purchase #4	$176.42	13.696%	$200.5825	$200.58	$200.60	$200.60
Purchase #5	$71.61	7.786%	$77.1856	$77.19	$77.20	$77.20
Purchase #6	$94.29	10.174%	$103.8831	$103.88	$103.90	$103.90
Purchase #7	$131.82	8.725%	$143.3213	$143.32	$143.30	$143.30
7 purchase totals =	$839.41		$937.4826	$937.48	$937.50	$937.50