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	$28.39	9.113%	$30.9772	$30.98	$31.00	$31.00
Purchase #2	$68.52	5.706%	$72.4298	$72.43	$72.45	$72.40
Purchase #3	$153.35	10.247%	$169.0638	$169.06	$169.05	$169.10
Purchase #4	$103.61	4.572%	$108.347	$108.35	$108.35	$108.30
Purchase #5	$27.98	6.627%	$29.8342	$29.83	$29.85	$29.80
Purchase #6	$112.73	7.238%	$120.8894	$120.89	$120.90	$120.90
Purchase #7	$172.35	4.651%	$180.366	$180.37	$180.35	$180.40
7 purchase totals =	$666.93		$711.9074	$711.91	$711.95	$711.90