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	$80.60	3.466%	$83.3936	$83.39	$83.40	$83.40
Purchase #2	$172.85	4.632%	$180.8564	$180.86	$180.85	$180.90
Purchase #3	$155.74	9.349%	$170.3001	$170.30	$170.30	$170.30
Purchase #4	$106.45	7.627%	$114.5689	$114.57	$114.55	$114.60
Purchase #5	$5.82	13.330%	$6.5958	$6.60	$6.60	$6.60
Purchase #6	$96.84	3.627%	$100.3524	$100.35	$100.35	$100.40
Purchase #7	$191.34	4.677%	$200.289	$200.29	$200.30	$200.30
7 purchase totals =	$809.64		$856.3562	$856.36	$856.35	$856.50