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	$242.35	5.864%	$256.5614	$256.56	$256.55	$256.60
Purchase #2	$39.60	8.155%	$42.8294	$42.83	$42.85	$42.80
Purchase #3	$131.78	6.868%	$140.8307	$140.83	$140.85	$140.80
Purchase #4	$137.84	11.798%	$154.1024	$154.10	$154.10	$154.10
Purchase #5	$154.87	12.108%	$173.6217	$173.62	$173.60	$173.60
Purchase #6	$199.51	11.402%	$222.2581	$222.26	$222.25	$222.30
Purchase #7	$125.90	11.372%	$140.2173	$140.22	$140.20	$140.20
7 purchase totals =	$1,031.85		$1,130.4210	$1,130.42	$1,130.40	$1,130.40