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	$42.76	10.539%	$47.2665	$47.27	$47.25	$47.30
Purchase #2	$51.68	3.202%	$53.3348	$53.33	$53.35	$53.30
Purchase #3	$71.94	6.816%	$76.8434	$76.84	$76.85	$76.80
Purchase #4	$132.98	9.849%	$146.0772	$146.08	$146.10	$146.10
Purchase #5	$214.99	9.249%	$234.8744	$234.87	$234.85	$234.90
Purchase #6	$159.94	5.408%	$168.5896	$168.59	$168.60	$168.60
Purchase #7	$60.81	3.421%	$62.8903	$62.89	$62.90	$62.90
7 purchase totals =	$735.10		$789.8762	$789.87	$789.90	$789.90