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	$139.70	3.392%	$144.4386	$144.44	$144.45	$144.40
Purchase #2	$172.72	8.544%	$187.4772	$187.48	$187.50	$187.50
Purchase #3	$154.72	6.392%	$164.6097	$164.61	$164.60	$164.60
Purchase #4	$71.86	11.442%	$80.0822	$80.08	$80.10	$80.10
Purchase #5	$58.83	7.847%	$63.4464	$63.45	$63.45	$63.40
Purchase #6	$163.44	6.205%	$173.5815	$173.58	$173.60	$173.60
Purchase #7	$232.29	13.870%	$264.5086	$264.51	$264.50	$264.50
7 purchase totals =	$993.56		$1,078.1442	$1,078.15	$1,078.20	$1,078.10