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	$154.31	8.823%	$167.9248	$167.92	$167.90	$167.90
Purchase #2	$200.25	13.160%	$226.6029	$226.60	$226.60	$226.60
Purchase #3	$155.95	8.182%	$168.7098	$168.71	$168.70	$168.70
Purchase #4	$17.93	12.110%	$20.1013	$20.10	$20.10	$20.10
Purchase #5	$82.95	5.250%	$87.3049	$87.30	$87.30	$87.30
Purchase #6	$81.59	9.627%	$89.4447	$89.44	$89.45	$89.40
Purchase #7	$60.35	9.195%	$65.8992	$65.90	$65.90	$65.90
7 purchase totals =	$753.33		$825.9876	$825.97	$825.95	$825.90