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	$98.60	10.765%	$109.2143	$109.21	$109.20	$109.20
Purchase #2	$161.48	5.177%	$169.8398	$169.84	$169.85	$169.80
Purchase #3	$49.49	4.516%	$51.725	$51.73	$51.75	$51.70
Purchase #4	$81.97	10.683%	$90.7269	$90.73	$90.75	$90.70
Purchase #5	$79.66	3.462%	$82.4178	$82.42	$82.40	$82.40
Purchase #6	$147.41	6.217%	$156.5745	$156.57	$156.55	$156.60
Purchase #7	$143.82	10.183%	$158.4652	$158.47	$158.45	$158.50
7 purchase totals =	$762.43		$818.9635	$818.97	$818.95	$818.90