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	$5.65	7.254%	$6.0599	$6.06	$6.05	$6.10
Purchase #2	$127.63	13.237%	$144.5244	$144.52	$144.50	$144.50
Purchase #3	$63.89	5.795%	$67.5924	$67.59	$67.60	$67.60
Purchase #4	$41.69	12.750%	$47.0055	$47.01	$47.00	$47.00
Purchase #5	$16.41	6.352%	$17.4524	$17.45	$17.45	$17.50
Purchase #6	$244.92	5.482%	$258.3465	$258.35	$258.35	$258.30
Purchase #7	$27.85	13.247%	$31.5393	$31.54	$31.55	$31.50
7 purchase totals =	$528.04		$572.5204	$572.52	$572.50	$572.50