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	$158.87	12.477%	$178.6922	$178.69	$178.70	$178.70
Purchase #2	$193.83	9.102%	$211.4724	$211.47	$211.45	$211.50
Purchase #3	$123.70	6.472%	$131.7059	$131.71	$131.70	$131.70
Purchase #4	$115.80	10.266%	$127.688	$127.69	$127.70	$127.70
Purchase #5	$30.67	6.476%	$32.6562	$32.66	$32.65	$32.70
Purchase #6	$43.61	5.394%	$45.9623	$45.96	$45.95	$46.00
Purchase #7	$46.37	7.748%	$49.9627	$49.96	$49.95	$50.00
7 purchase totals =	$712.85		$778.1397	$778.14	$778.10	$778.30