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	$243.39	6.836%	$260.0281	$260.03	$260.05	$260.00
Purchase #2	$70.61	13.836%	$80.3796	$80.38	$80.40	$80.40
Purchase #3	$34.38	6.105%	$36.4789	$36.48	$36.50	$36.50
Purchase #4	$76.64	12.296%	$86.0637	$86.06	$86.05	$86.10
Purchase #5	$81.66	10.486%	$90.2229	$90.22	$90.20	$90.20
Purchase #6	$11.64	10.532%	$12.8659	$12.87	$12.85	$12.90
Purchase #7	$141.60	12.630%	$159.4841	$159.48	$159.50	$159.50
7 purchase totals =	$659.92		$725.5232	$725.52	$725.55	$725.60