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	$67.59	7.408%	$72.5971	$72.60	$72.60	$72.60
Purchase #2	$147.44	11.768%	$164.7907	$164.79	$164.80	$164.80
Purchase #3	$148.42	3.140%	$153.0804	$153.08	$153.10	$153.10
Purchase #4	$69.73	3.873%	$72.4306	$72.43	$72.45	$72.40
Purchase #5	$55.88	13.720%	$63.5467	$63.55	$63.55	$63.50
Purchase #6	$47.33	6.782%	$50.5399	$50.54	$50.55	$50.50
Purchase #7	$52.85	9.212%	$57.7185	$57.72	$57.70	$57.70
7 purchase totals =	$589.24		$634.7039	$634.71	$634.75	$634.60