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	$100.72	6.751%	$107.5196	$107.52	$107.50	$107.50
Purchase #2	$75.38	12.766%	$85.003	$85.00	$85.00	$85.00
Purchase #3	$102.75	11.561%	$114.6289	$114.63	$114.65	$114.60
Purchase #4	$47.82	10.533%	$52.8569	$52.86	$52.85	$52.90
Purchase #5	$121.26	11.232%	$134.8799	$134.88	$134.90	$134.90
Purchase #6	$154.60	6.530%	$164.6954	$164.70	$164.70	$164.70
Purchase #7	$24.84	13.755%	$28.2567	$28.26	$28.25	$28.30
7 purchase totals =	$627.37		$687.8404	$687.85	$687.85	$687.90