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	$20.71	6.671%	$22.0916	$22.09	$22.10	$22.10
Purchase #2	$122.38	8.746%	$133.0834	$133.08	$133.10	$133.10
Purchase #3	$21.31	7.224%	$22.8494	$22.85	$22.85	$22.80
Purchase #4	$34.83	12.736%	$39.2659	$39.27	$39.25	$39.30
Purchase #5	$162.88	7.783%	$175.557	$175.56	$175.55	$175.60
Purchase #6	$120.81	8.826%	$131.4727	$131.47	$131.45	$131.50
Purchase #7	$130.58	9.126%	$142.4967	$142.50	$142.50	$142.50
7 purchase totals =	$613.50		$666.8167	$666.82	$666.80	$666.90