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	$50.86	11.791%	$56.8569	$56.86	$56.85	$56.90
Purchase #2	$86.89	3.550%	$89.9746	$89.97	$89.95	$90.00
Purchase #3	$236.67	13.144%	$267.7779	$267.78	$267.80	$267.80
Purchase #4	$28.35	4.156%	$29.5282	$29.53	$29.55	$29.50
Purchase #5	$208.89	13.276%	$236.6222	$236.62	$236.60	$236.60
Purchase #6	$241.75	8.518%	$262.3423	$262.34	$262.35	$262.30
Purchase #7	$60.88	4.332%	$63.5173	$63.52	$63.50	$63.50
7 purchase totals =	$914.29		$1,006.6194	$1,006.62	$1,006.60	$1,006.60