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	$6.45	6.560%	$6.8731	$6.87	$6.85	$6.90
Purchase #2	$136.80	4.739%	$143.283	$143.28	$143.30	$143.30
Purchase #3	$119.47	3.409%	$123.5427	$123.54	$123.55	$123.50
Purchase #4	$130.52	11.631%	$145.7008	$145.70	$145.70	$145.70
Purchase #5	$176.86	4.490%	$184.801	$184.80	$184.80	$184.80
Purchase #6	$183.93	3.578%	$190.511	$190.51	$190.50	$190.50
Purchase #7	$127.33	8.799%	$138.5338	$138.53	$138.55	$138.50
7 purchase totals =	$881.36		$933.2454	$933.23	$933.25	$933.20