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	$29.94	5.838%	$31.6879	$31.69	$31.70	$31.70
Purchase #2	$116.47	9.865%	$127.9598	$127.96	$127.95	$128.00
Purchase #3	$183.38	11.132%	$203.7939	$203.79	$203.80	$203.80
Purchase #4	$95.95	10.654%	$106.1725	$106.17	$106.15	$106.20
Purchase #5	$241.83	11.623%	$269.9379	$269.94	$269.95	$269.90
Purchase #6	$131.67	6.191%	$139.8217	$139.82	$139.80	$139.80
Purchase #7	$172.70	13.693%	$196.3478	$196.35	$196.35	$196.30
7 purchase totals =	$971.94		$1,075.7215	$1,075.72	$1,075.70	$1,075.70