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	$166.77	5.746%	$176.3526	$176.35	$176.35	$176.40
Purchase #2	$36.49	11.293%	$40.6108	$40.61	$40.60	$40.60
Purchase #3	$188.89	8.162%	$204.3072	$204.31	$204.30	$204.30
Purchase #4	$178.81	7.699%	$192.5766	$192.58	$192.60	$192.60
Purchase #5	$5.76	13.522%	$6.5389	$6.54	$6.55	$6.50
Purchase #6	$37.79	11.202%	$42.0232	$42.02	$42.00	$42.00
Purchase #7	$16.37	10.682%	$18.1186	$18.12	$18.10	$18.10
7 purchase totals =	$630.88		$680.5279	$680.53	$680.50	$680.50