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	$131.46	6.691%	$140.256	$140.26	$140.25	$140.30
Purchase #2	$156.74	7.531%	$168.5441	$168.54	$168.55	$168.50
Purchase #3	$107.65	11.254%	$119.7649	$119.76	$119.75	$119.80
Purchase #4	$20.60	4.535%	$21.5342	$21.53	$21.55	$21.50
Purchase #5	$244.84	7.421%	$263.0096	$263.01	$263.00	$263.00
Purchase #6	$77.97	5.467%	$82.2326	$82.23	$82.25	$82.20
Purchase #7	$241.58	12.217%	$271.0938	$271.09	$271.10	$271.10
7 purchase totals =	$980.84		$1,066.4352	$1,066.42	$1,066.45	$1,066.40