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	$20.51	9.719%	$22.5034	$22.50	$22.50	$22.50
Purchase #2	$123.38	9.307%	$134.863	$134.86	$134.85	$134.90
Purchase #3	$53.28	11.225%	$59.2607	$59.26	$59.25	$59.30
Purchase #4	$156.89	10.280%	$173.0183	$173.02	$173.00	$173.00
Purchase #5	$181.82	11.697%	$203.0875	$203.09	$203.10	$203.10
Purchase #6	$164.43	8.580%	$178.5381	$178.54	$178.55	$178.50
Purchase #7	$153.85	11.495%	$171.5351	$171.54	$171.55	$171.50
7 purchase totals =	$854.16		$942.8061	$942.81	$942.80	$942.80