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	$159.92	8.756%	$173.9226	$173.92	$173.90	$173.90
Purchase #2	$99.33	12.266%	$111.5138	$111.51	$111.50	$111.50
Purchase #3	$102.67	9.301%	$112.2193	$112.22	$112.20	$112.20
Purchase #4	$64.90	5.789%	$68.6571	$68.66	$68.65	$68.70
Purchase #5	$97.86	11.196%	$108.8164	$108.82	$108.80	$108.80
Purchase #6	$66.41	3.644%	$68.83	$68.83	$68.85	$68.80
Purchase #7	$193.65	3.653%	$200.724	$200.72	$200.70	$200.70
7 purchase totals =	$784.74		$844.6832	$844.68	$844.60	$844.60