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	$171.35	8.776%	$186.3877	$186.39	$186.40	$186.40
Purchase #2	$90.79	13.451%	$103.0022	$103.00	$103.00	$103.00
Purchase #3	$138.25	10.549%	$152.834	$152.83	$152.85	$152.80
Purchase #4	$226.38	5.335%	$238.4574	$238.46	$238.45	$238.50
Purchase #5	$84.68	10.508%	$93.5782	$93.58	$93.60	$93.60
Purchase #6	$168.68	7.807%	$181.8488	$181.85	$181.85	$181.80
Purchase #7	$232.33	5.359%	$244.7806	$244.78	$244.80	$244.80
7 purchase totals =	$1,112.46		$1,200.8889	$1,200.89	$1,200.95	$1,200.90