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	$148.97	5.363%	$156.9593	$156.96	$156.95	$157.00
Purchase #2	$112.45	9.508%	$123.1417	$123.14	$123.15	$123.10
Purchase #3	$234.70	9.857%	$257.8344	$257.83	$257.85	$257.80
Purchase #4	$48.25	13.229%	$54.633	$54.63	$54.65	$54.60
Purchase #5	$131.80	8.558%	$143.0794	$143.08	$143.10	$143.10
Purchase #6	$237.90	4.713%	$249.1122	$249.11	$249.10	$249.10
Purchase #7	$87.28	3.666%	$90.4797	$90.48	$90.50	$90.50
7 purchase totals =	$1,001.35		$1,075.2397	$1,075.23	$1,075.30	$1,075.20