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	$107.64	9.267%	$117.615	$117.62	$117.60	$117.60
Purchase #2	$216.65	11.178%	$240.8671	$240.87	$240.85	$240.90
Purchase #3	$80.78	12.559%	$90.9252	$90.93	$90.95	$90.90
Purchase #4	$200.89	12.158%	$225.3142	$225.31	$225.30	$225.30
Purchase #5	$122.80	12.286%	$137.8872	$137.89	$137.90	$137.90
Purchase #6	$212.53	3.522%	$220.0153	$220.02	$220.00	$220.00
Purchase #7	$138.72	12.249%	$155.7118	$155.71	$155.70	$155.70
7 purchase totals =	$1,080.01		$1,188.3358	$1,188.35	$1,188.30	$1,188.30