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	$128.85	13.748%	$146.5643	$146.56	$146.55	$146.60
Purchase #2	$225.64	4.239%	$235.2049	$235.20	$235.20	$235.20
Purchase #3	$154.43	6.635%	$164.6764	$164.68	$164.70	$164.70
Purchase #4	$208.55	5.152%	$219.2945	$219.29	$219.30	$219.30
Purchase #5	$237.90	8.528%	$258.1881	$258.19	$258.20	$258.20
Purchase #6	$119.83	12.272%	$134.5355	$134.54	$134.55	$134.50
Purchase #7	$137.73	3.388%	$142.3963	$142.40	$142.40	$142.40
7 purchase totals =	$1,212.93		$1,300.8600	$1,300.86	$1,300.90	$1,300.90