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	$51.96	9.593%	$56.9445	$56.94	$56.95	$56.90
Purchase #2	$82.92	5.335%	$87.3438	$87.34	$87.35	$87.30
Purchase #3	$172.28	10.630%	$190.5934	$190.59	$190.60	$190.60
Purchase #4	$73.29	9.536%	$80.2789	$80.28	$80.30	$80.30
Purchase #5	$201.26	11.809%	$225.0268	$225.03	$225.05	$225.00
Purchase #6	$132.40	11.765%	$147.9769	$147.98	$148.00	$148.00
Purchase #7	$53.93	13.592%	$61.2602	$61.26	$61.25	$61.30
7 purchase totals =	$768.04		$849.4245	$849.42	$849.50	$849.40