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	$54.70	7.858%	$58.9983	$59.00	$59.00	$59.00
Purchase #2	$108.90	13.143%	$123.2127	$123.21	$123.20	$123.20
Purchase #3	$205.47	4.836%	$215.4065	$215.41	$215.40	$215.40
Purchase #4	$231.29	13.307%	$262.0678	$262.07	$262.05	$262.10
Purchase #5	$201.67	7.821%	$217.4426	$217.44	$217.45	$217.40
Purchase #6	$95.74	8.440%	$103.8205	$103.82	$103.80	$103.80
Purchase #7	$24.90	12.452%	$28.0005	$28.00	$28.00	$28.00
7 purchase totals =	$922.67		$1,008.9489	$1,008.95	$1,008.90	$1,008.90