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	$87.39	3.183%	$90.1716	$90.17	$90.15	$90.20
Purchase #2	$164.77	11.293%	$183.3775	$183.38	$183.40	$183.40
Purchase #3	$214.42	5.231%	$225.6363	$225.64	$225.65	$225.60
Purchase #4	$132.54	6.357%	$140.9656	$140.97	$140.95	$141.00
Purchase #5	$224.68	7.726%	$242.0388	$242.04	$242.05	$242.00
Purchase #6	$180.84	5.523%	$190.8278	$190.83	$190.85	$190.80
Purchase #7	$94.84	6.279%	$100.795	$100.80	$100.80	$100.80
7 purchase totals =	$1,099.48		$1,173.8126	$1,173.83	$1,173.85	$1,173.80