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	$144.29	12.436%	$162.2339	$162.23	$162.25	$162.20
Purchase #2	$74.83	11.788%	$83.651	$83.65	$83.65	$83.70
Purchase #3	$38.52	4.666%	$40.3173	$40.32	$40.30	$40.30
Purchase #4	$118.60	5.335%	$124.9273	$124.93	$124.95	$124.90
Purchase #5	$70.27	9.686%	$77.0764	$77.08	$77.10	$77.10
Purchase #6	$59.29	13.153%	$67.0884	$67.09	$67.10	$67.10
Purchase #7	$205.67	8.207%	$222.5493	$222.55	$222.55	$222.50
7 purchase totals =	$711.47		$777.8436	$777.85	$777.90	$777.80