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	$103.63	5.268%	$109.0892	$109.09	$109.10	$109.10
Purchase #2	$83.95	11.337%	$93.4674	$93.47	$93.45	$93.50
Purchase #3	$215.93	8.666%	$234.6425	$234.64	$234.65	$234.60
Purchase #4	$35.64	8.178%	$38.5546	$38.55	$38.55	$38.60
Purchase #5	$233.85	12.152%	$262.2675	$262.27	$262.25	$262.30
Purchase #6	$237.94	13.828%	$270.8423	$270.84	$270.85	$270.80
Purchase #7	$81.78	10.442%	$90.3195	$90.32	$90.30	$90.30
7 purchase totals =	$992.72		$1,099.1830	$1,099.18	$1,099.15	$1,099.20