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	$160.85	3.564%	$166.5827	$166.58	$166.60	$166.60
Purchase #2	$18.67	9.865%	$20.5118	$20.51	$20.50	$20.50
Purchase #3	$230.83	10.402%	$254.8409	$254.84	$254.85	$254.80
Purchase #4	$200.68	8.341%	$217.4187	$217.42	$217.40	$217.40
Purchase #5	$137.65	9.639%	$150.9181	$150.92	$150.90	$150.90
Purchase #6	$127.60	13.110%	$144.3284	$144.33	$144.35	$144.30
Purchase #7	$200.68	12.841%	$226.4493	$226.45	$226.45	$226.40
7 purchase totals =	$1,076.96		$1,181.0499	$1,181.05	$1,181.05	$1,180.90