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	$34.51	11.807%	$38.5846	$38.58	$38.60	$38.60
Purchase #2	$181.49	3.526%	$187.8893	$187.89	$187.90	$187.90
Purchase #3	$33.78	9.278%	$36.9141	$36.91	$36.90	$36.90
Purchase #4	$85.52	4.363%	$89.2512	$89.25	$89.25	$89.30
Purchase #5	$143.52	6.870%	$153.3798	$153.38	$153.40	$153.40
Purchase #6	$102.80	9.615%	$112.6842	$112.68	$112.70	$112.70
Purchase #7	$199.26	4.544%	$208.3144	$208.31	$208.30	$208.30
7 purchase totals =	$780.88		$827.0176	$827.00	$827.05	$827.10