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	$144.56	10.264%	$159.3976	$159.40	$159.40	$159.40
Purchase #2	$71.35	12.660%	$80.3829	$80.38	$80.40	$80.40
Purchase #3	$71.52	6.468%	$76.1459	$76.15	$76.15	$76.10
Purchase #4	$21.79	13.672%	$24.7691	$24.77	$24.75	$24.80
Purchase #5	$151.81	10.587%	$167.8821	$167.88	$167.90	$167.90
Purchase #6	$78.73	4.793%	$82.5035	$82.50	$82.50	$82.50
Purchase #7	$24.99	9.691%	$27.4118	$27.41	$27.40	$27.40
7 purchase totals =	$564.75		$618.4929	$618.49	$618.50	$618.50