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	$109.25	12.126%	$122.4977	$122.50	$122.50	$122.50
Purchase #2	$58.54	10.248%	$64.5392	$64.54	$64.55	$64.50
Purchase #3	$227.39	10.162%	$250.4974	$250.50	$250.50	$250.50
Purchase #4	$93.51	6.706%	$99.7808	$99.78	$99.80	$99.80
Purchase #5	$19.32	3.579%	$20.0115	$20.01	$20.00	$20.00
Purchase #6	$228.48	12.236%	$256.4368	$256.44	$256.45	$256.40
Purchase #7	$56.28	11.182%	$62.5732	$62.57	$62.55	$62.60
7 purchase totals =	$792.77		$876.3366	$876.34	$876.35	$876.30