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	$241.50	10.392%	$266.5967	$266.60	$266.60	$266.60
Purchase #2	$126.40	10.837%	$140.098	$140.10	$140.10	$140.10
Purchase #3	$38.44	3.104%	$39.6332	$39.63	$39.65	$39.60
Purchase #4	$120.77	8.681%	$131.254	$131.25	$131.25	$131.30
Purchase #5	$136.86	5.280%	$144.0862	$144.09	$144.10	$144.10
Purchase #6	$160.98	4.374%	$168.0213	$168.02	$168.00	$168.00
Purchase #7	$80.85	13.363%	$91.654	$91.65	$91.65	$91.70
7 purchase totals =	$905.80		$981.3434	$981.34	$981.35	$981.40