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	$80.82	12.137%	$90.6291	$90.63	$90.65	$90.60
Purchase #2	$162.25	3.153%	$167.3657	$167.37	$167.35	$167.40
Purchase #3	$169.93	10.532%	$187.827	$187.83	$187.85	$187.80
Purchase #4	$47.35	10.126%	$52.1447	$52.14	$52.15	$52.10
Purchase #5	$8.54	4.264%	$8.9041	$8.90	$8.90	$8.90
Purchase #6	$249.41	10.863%	$276.5034	$276.50	$276.50	$276.50
Purchase #7	$115.37	10.250%	$127.1954	$127.20	$127.20	$127.20
7 purchase totals =	$833.67		$910.5694	$910.57	$910.60	$910.50