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	$203.51	9.395%	$222.6298	$222.63	$222.65	$222.60
Purchase #2	$69.77	11.845%	$78.0343	$78.03	$78.05	$78.00
Purchase #3	$54.77	5.212%	$57.6246	$57.62	$57.60	$57.60
Purchase #4	$95.32	9.268%	$104.1543	$104.15	$104.15	$104.20
Purchase #5	$77.31	5.560%	$81.6084	$81.61	$81.60	$81.60
Purchase #6	$174.99	13.182%	$198.0572	$198.06	$198.05	$198.10
Purchase #7	$148.35	6.116%	$157.4231	$157.42	$157.40	$157.40
7 purchase totals =	$824.02		$899.5317	$899.52	$899.50	$899.50