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	$74.82	10.465%	$82.6499	$82.65	$82.65	$82.60
Purchase #2	$105.60	3.147%	$108.9232	$108.92	$108.90	$108.90
Purchase #3	$125.88	13.473%	$142.8398	$142.84	$142.85	$142.80
Purchase #4	$188.77	10.832%	$209.2176	$209.22	$209.20	$209.20
Purchase #5	$227.67	4.287%	$237.4302	$237.43	$237.45	$237.40
Purchase #6	$52.32	3.858%	$54.3385	$54.34	$54.35	$54.30
Purchase #7	$242.39	8.493%	$262.9762	$262.98	$263.00	$263.00
7 purchase totals =	$1,017.45		$1,098.3754	$1,098.38	$1,098.40	$1,098.20