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	$228.97	5.330%	$241.1741	$241.17	$241.15	$241.20
Purchase #2	$59.28	10.129%	$65.2845	$65.28	$65.30	$65.30
Purchase #3	$47.90	13.149%	$54.1984	$54.20	$54.20	$54.20
Purchase #4	$95.90	8.307%	$103.8664	$103.87	$103.85	$103.90
Purchase #5	$18.80	10.775%	$20.8257	$20.83	$20.85	$20.80
Purchase #6	$40.53	12.345%	$45.5334	$45.53	$45.55	$45.50
Purchase #7	$123.63	8.746%	$134.4427	$134.44	$134.45	$134.40
7 purchase totals =	$615.01		$665.3252	$665.32	$665.35	$665.30