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	$126.69	10.166%	$139.5693	$139.57	$139.55	$139.60
Purchase #2	$199.82	12.516%	$224.8295	$224.83	$224.85	$224.80
Purchase #3	$227.36	12.545%	$255.8823	$255.88	$255.90	$255.90
Purchase #4	$250.72	11.829%	$280.3777	$280.38	$280.40	$280.40
Purchase #5	$73.28	9.719%	$80.4021	$80.40	$80.40	$80.40
Purchase #6	$171.37	10.659%	$189.6363	$189.64	$189.65	$189.60
Purchase #7	$214.48	12.118%	$240.4707	$240.47	$240.45	$240.50
7 purchase totals =	$1,263.72		$1,411.1679	$1,411.17	$1,411.20	$1,411.20