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	$144.94	12.128%	$162.5183	$162.52	$162.50	$162.50
Purchase #2	$38.25	13.698%	$43.4895	$43.49	$43.50	$43.50
Purchase #3	$18.87	3.414%	$19.5142	$19.51	$19.50	$19.50
Purchase #4	$214.31	4.720%	$224.4254	$224.43	$224.45	$224.40
Purchase #5	$244.47	10.692%	$270.6087	$270.61	$270.60	$270.60
Purchase #6	$69.68	9.154%	$76.0585	$76.06	$76.05	$76.10
Purchase #7	$160.27	12.866%	$180.8903	$180.89	$180.90	$180.90
7 purchase totals =	$890.79		$977.5049	$977.51	$977.50	$977.50