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	$30.59	9.850%	$33.6031	$33.60	$33.60	$33.60
Purchase #2	$237.68	10.112%	$261.7142	$261.71	$261.70	$261.70
Purchase #3	$87.68	3.603%	$90.8391	$90.84	$90.85	$90.80
Purchase #4	$164.78	3.692%	$170.8637	$170.86	$170.85	$170.90
Purchase #5	$57.30	10.645%	$63.3996	$63.40	$63.40	$63.40
Purchase #6	$46.37	12.130%	$51.9947	$51.99	$52.00	$52.00
Purchase #7	$160.70	7.109%	$172.1242	$172.12	$172.10	$172.10
7 purchase totals =	$785.10		$844.5386	$844.52	$844.50	$844.50