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	$90.32	11.268%	$100.4973	$100.50	$100.50	$100.50
Purchase #2	$145.47	9.645%	$159.5006	$159.50	$159.50	$159.50
Purchase #3	$21.54	13.628%	$24.4755	$24.48	$24.50	$24.50
Purchase #4	$128.80	11.710%	$143.8825	$143.88	$143.90	$143.90
Purchase #5	$133.98	7.212%	$143.6426	$143.64	$143.65	$143.60
Purchase #6	$199.84	9.195%	$218.2153	$218.22	$218.20	$218.20
Purchase #7	$183.30	13.597%	$208.2233	$208.22	$208.20	$208.20
7 purchase totals =	$903.25		$998.4371	$998.44	$998.45	$998.40