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	$20.32	9.775%	$22.3063	$22.31	$22.30	$22.30
Purchase #2	$26.50	3.520%	$27.4328	$27.43	$27.45	$27.40
Purchase #3	$61.29	7.506%	$65.8904	$65.89	$65.90	$65.90
Purchase #4	$90.75	7.612%	$97.6579	$97.66	$97.65	$97.70
Purchase #5	$167.52	12.139%	$187.8553	$187.86	$187.85	$187.90
Purchase #6	$142.49	9.405%	$155.8912	$155.89	$155.90	$155.90
Purchase #7	$144.79	5.145%	$152.2394	$152.24	$152.25	$152.20
7 purchase totals =	$653.66		$709.2733	$709.28	$709.30	$709.30