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	$11.32	12.860%	$12.7758	$12.78	$12.80	$12.80
Purchase #2	$36.54	4.757%	$38.2782	$38.28	$38.30	$38.30
Purchase #3	$248.57	10.632%	$274.998	$275.00	$275.00	$275.00
Purchase #4	$123.46	11.679%	$137.8789	$137.88	$137.90	$137.90
Purchase #5	$164.82	7.271%	$176.8041	$176.80	$176.80	$176.80
Purchase #6	$51.37	12.858%	$57.9752	$57.98	$58.00	$58.00
Purchase #7	$122.38	7.757%	$131.873	$131.87	$131.85	$131.90
7 purchase totals =	$758.46		$830.5832	$830.59	$830.65	$830.70