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	$91.55	13.514%	$103.9221	$103.92	$103.90	$103.90
Purchase #2	$82.31	3.866%	$85.4921	$85.49	$85.50	$85.50
Purchase #3	$127.60	4.659%	$133.5449	$133.54	$133.55	$133.50
Purchase #4	$32.36	3.418%	$33.4661	$33.47	$33.45	$33.50
Purchase #5	$96.86	3.341%	$100.0961	$100.10	$100.10	$100.10
Purchase #6	$226.67	12.806%	$255.6974	$255.70	$255.70	$255.70
Purchase #7	$198.37	5.179%	$208.6436	$208.64	$208.65	$208.60
7 purchase totals =	$855.72		$920.8623	$920.86	$920.85	$920.80