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	$218.89	10.284%	$241.4006	$241.40	$241.40	$241.40
Purchase #2	$105.40	5.615%	$111.3182	$111.32	$111.30	$111.30
Purchase #3	$97.72	6.452%	$104.0249	$104.02	$104.00	$104.00
Purchase #4	$131.25	7.125%	$140.6016	$140.60	$140.60	$140.60
Purchase #5	$164.29	3.630%	$170.2537	$170.25	$170.25	$170.30
Purchase #6	$177.88	6.226%	$188.9548	$188.95	$188.95	$189.00
Purchase #7	$82.92	4.248%	$86.4424	$86.44	$86.45	$86.40
7 purchase totals =	$978.35		$1,042.9962	$1,042.98	$1,042.95	$1,043.00