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	$142.76	9.513%	$156.3408	$156.34	$156.35	$156.30
Purchase #2	$126.94	8.725%	$138.0155	$138.02	$138.00	$138.00
Purchase #3	$44.30	8.268%	$47.9627	$47.96	$47.95	$48.00
Purchase #4	$61.46	7.861%	$66.2914	$66.29	$66.30	$66.30
Purchase #5	$29.45	9.264%	$32.1782	$32.18	$32.20	$32.20
Purchase #6	$83.48	7.692%	$89.9013	$89.90	$89.90	$89.90
Purchase #7	$98.68	13.292%	$111.7965	$111.80	$111.80	$111.80
7 purchase totals =	$587.07		$642.4864	$642.49	$642.50	$642.50