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	$194.30	12.481%	$218.5506	$218.55	$218.55	$218.60
Purchase #2	$63.89	4.427%	$66.7184	$66.72	$66.70	$66.70
Purchase #3	$134.42	6.730%	$143.4665	$143.47	$143.45	$143.50
Purchase #4	$103.54	11.578%	$115.5279	$115.53	$115.55	$115.50
Purchase #5	$61.61	8.102%	$66.6016	$66.60	$66.60	$66.60
Purchase #6	$62.95	5.329%	$66.3046	$66.30	$66.30	$66.30
Purchase #7	$98.45	11.416%	$109.6891	$109.69	$109.70	$109.70
7 purchase totals =	$719.16		$786.8587	$786.86	$786.85	$786.90