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	$9.80	13.601%	$11.1329	$11.13	$11.15	$11.10
Purchase #2	$11.74	7.306%	$12.5977	$12.60	$12.60	$12.60
Purchase #3	$121.39	4.135%	$126.4095	$126.41	$126.40	$126.40
Purchase #4	$97.55	4.484%	$101.9241	$101.92	$101.90	$101.90
Purchase #5	$46.51	8.653%	$50.5345	$50.53	$50.55	$50.50
Purchase #6	$127.72	7.191%	$136.9043	$136.90	$136.90	$136.90
Purchase #7	$92.88	7.561%	$99.9027	$99.90	$99.90	$99.90
7 purchase totals =	$507.59		$539.4057	$539.39	$539.40	$539.30