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	$123.81	13.708%	$140.7819	$140.78	$140.80	$140.80
Purchase #2	$38.83	4.344%	$40.5168	$40.52	$40.50	$40.50
Purchase #3	$196.81	9.657%	$215.8159	$215.82	$215.80	$215.80
Purchase #4	$89.72	5.123%	$94.3164	$94.32	$94.30	$94.30
Purchase #5	$126.79	8.509%	$137.5786	$137.58	$137.60	$137.60
Purchase #6	$248.49	4.577%	$259.8634	$259.86	$259.85	$259.90
Purchase #7	$32.56	12.797%	$36.7267	$36.73	$36.75	$36.70
7 purchase totals =	$857.01		$925.5997	$925.61	$925.60	$925.60