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	$6.75	10.801%	$7.4791	$7.48	$7.50	$7.50
Purchase #2	$34.87	4.713%	$36.5134	$36.51	$36.50	$36.50
Purchase #3	$144.52	6.795%	$154.3401	$154.34	$154.35	$154.30
Purchase #4	$82.68	12.344%	$92.886	$92.89	$92.90	$92.90
Purchase #5	$59.52	9.352%	$65.0863	$65.09	$65.10	$65.10
Purchase #6	$200.65	5.454%	$211.5935	$211.59	$211.60	$211.60
Purchase #7	$71.83	9.291%	$78.5037	$78.50	$78.50	$78.50
7 purchase totals =	$600.82		$646.4021	$646.40	$646.45	$646.40