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	$89.92	9.459%	$98.4255	$98.43	$98.45	$98.40
Purchase #2	$111.96	3.435%	$115.8058	$115.81	$115.80	$115.80
Purchase #3	$205.64	10.527%	$227.2877	$227.29	$227.30	$227.30
Purchase #4	$75.34	12.264%	$84.5797	$84.58	$84.60	$84.60
Purchase #5	$28.58	11.206%	$31.7827	$31.78	$31.80	$31.80
Purchase #6	$102.71	8.606%	$111.5492	$111.55	$111.55	$111.50
Purchase #7	$172.71	8.282%	$187.0138	$187.01	$187.00	$187.00
7 purchase totals =	$786.86		$856.4444	$856.45	$856.50	$856.40