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	$56.42	5.591%	$59.5744	$59.57	$59.55	$59.60
Purchase #2	$76.46	8.709%	$83.1189	$83.12	$83.10	$83.10
Purchase #3	$128.94	11.639%	$143.9473	$143.95	$143.95	$143.90
Purchase #4	$186.37	4.719%	$195.1648	$195.16	$195.15	$195.20
Purchase #5	$147.83	10.629%	$163.5429	$163.54	$163.55	$163.50
Purchase #6	$95.99	4.748%	$100.5476	$100.55	$100.55	$100.50
Purchase #7	$139.97	11.784%	$156.4641	$156.46	$156.45	$156.50
7 purchase totals =	$831.98		$902.3600	$902.35	$902.30	$902.30