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	$85.32	6.530%	$90.8914	$90.89	$90.90	$90.90
Purchase #2	$129.67	9.864%	$142.4606	$142.46	$142.45	$142.50
Purchase #3	$207.99	9.133%	$226.9857	$226.99	$227.00	$227.00
Purchase #4	$249.55	5.328%	$262.846	$262.85	$262.85	$262.80
Purchase #5	$41.90	7.692%	$45.1229	$45.12	$45.10	$45.10
Purchase #6	$5.35	3.575%	$5.5413	$5.54	$5.55	$5.50
Purchase #7	$111.45	10.636%	$123.3038	$123.30	$123.30	$123.30
7 purchase totals =	$831.23		$897.1517	$897.15	$897.15	$897.10