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	$57.85	3.657%	$59.9656	$59.97	$59.95	$60.00
Purchase #2	$240.39	7.122%	$257.5106	$257.51	$257.50	$257.50
Purchase #3	$100.72	7.711%	$108.4865	$108.49	$108.50	$108.50
Purchase #4	$87.75	13.843%	$99.8972	$99.90	$99.90	$99.90
Purchase #5	$125.85	5.536%	$132.8171	$132.82	$132.80	$132.80
Purchase #6	$136.99	5.222%	$144.1436	$144.14	$144.15	$144.10
Purchase #7	$98.97	4.626%	$103.5484	$103.55	$103.55	$103.50
7 purchase totals =	$848.52		$906.3690	$906.38	$906.35	$906.30