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	$123.87	9.865%	$136.0898	$136.09	$136.10	$136.10
Purchase #2	$37.90	6.288%	$40.2832	$40.28	$40.30	$40.30
Purchase #3	$157.54	10.378%	$173.8895	$173.89	$173.90	$173.90
Purchase #4	$194.92	7.849%	$210.2193	$210.22	$210.20	$210.20
Purchase #5	$27.72	13.815%	$31.5495	$31.55	$31.55	$31.50
Purchase #6	$70.86	13.612%	$80.5055	$80.51	$80.50	$80.50
Purchase #7	$132.51	6.798%	$141.518	$141.52	$141.50	$141.50
7 purchase totals =	$745.32		$814.0548	$814.06	$814.05	$814.00