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	$43.45	4.744%	$45.5113	$45.51	$45.50	$45.50
Purchase #2	$171.60	8.202%	$185.6746	$185.67	$185.65	$185.70
Purchase #3	$112.94	13.419%	$128.0954	$128.10	$128.10	$128.10
Purchase #4	$48.35	10.372%	$53.3649	$53.36	$53.35	$53.40
Purchase #5	$33.74	8.242%	$36.5209	$36.52	$36.50	$36.50
Purchase #6	$47.90	9.803%	$52.5956	$52.60	$52.60	$52.60
Purchase #7	$21.85	13.232%	$24.7412	$24.74	$24.75	$24.70
7 purchase totals =	$479.83		$526.5039	$526.50	$526.45	$526.50