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	$120.83	6.506%	$128.6912	$128.69	$128.70	$128.70
Purchase #2	$104.77	13.746%	$119.1717	$119.17	$119.15	$119.20
Purchase #3	$98.25	7.189%	$105.3132	$105.31	$105.30	$105.30
Purchase #4	$127.37	12.685%	$143.5269	$143.53	$143.55	$143.50
Purchase #5	$203.25	13.483%	$230.6542	$230.65	$230.65	$230.70
Purchase #6	$131.66	7.413%	$141.42	$141.42	$141.40	$141.40
Purchase #7	$217.89	10.814%	$241.4526	$241.45	$241.45	$241.50
7 purchase totals =	$1,004.02		$1,110.2298	$1,110.22	$1,110.20	$1,110.30