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	$51.38	10.326%	$56.6855	$56.69	$56.70	$56.70
Purchase #2	$238.29	8.367%	$258.2277	$258.23	$258.25	$258.20
Purchase #3	$67.77	7.349%	$72.7504	$72.75	$72.75	$72.80
Purchase #4	$160.78	3.786%	$166.8671	$166.87	$166.85	$166.90
Purchase #5	$194.63	9.718%	$213.5441	$213.54	$213.55	$213.50
Purchase #6	$78.83	10.163%	$86.8415	$86.84	$86.85	$86.80
Purchase #7	$12.63	6.868%	$13.4974	$13.50	$13.50	$13.50
7 purchase totals =	$804.31		$868.4137	$868.42	$868.45	$868.40