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	$32.92	3.818%	$34.1769	$34.18	$34.20	$34.20
Purchase #2	$45.52	5.272%	$47.9198	$47.92	$47.90	$47.90
Purchase #3	$239.80	6.821%	$256.1568	$256.16	$256.15	$256.20
Purchase #4	$72.54	8.267%	$78.5369	$78.54	$78.55	$78.50
Purchase #5	$132.52	4.554%	$138.555	$138.56	$138.55	$138.60
Purchase #6	$45.98	11.617%	$51.3215	$51.32	$51.30	$51.30
Purchase #7	$188.42	12.457%	$211.8915	$211.89	$211.90	$211.90
7 purchase totals =	$757.70		$818.5584	$818.57	$818.55	$818.60