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	$79.97	9.611%	$87.6559	$87.66	$87.65	$87.70
Purchase #2	$111.88	10.212%	$123.3052	$123.31	$123.30	$123.30
Purchase #3	$38.64	12.362%	$43.4167	$43.42	$43.40	$43.40
Purchase #4	$29.60	10.383%	$32.6734	$32.67	$32.65	$32.70
Purchase #5	$89.62	12.565%	$100.8808	$100.88	$100.90	$100.90
Purchase #6	$37.68	6.311%	$40.058	$40.06	$40.05	$40.10
Purchase #7	$229.58	11.488%	$255.9542	$255.95	$255.95	$256.00
7 purchase totals =	$616.97		$683.9442	$683.95	$683.90	$684.10