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	$109.87	12.147%	$123.2159	$123.22	$123.20	$123.20
Purchase #2	$205.86	11.509%	$229.5524	$229.55	$229.55	$229.60
Purchase #3	$38.70	7.656%	$41.6629	$41.66	$41.65	$41.70
Purchase #4	$183.26	4.243%	$191.0357	$191.04	$191.05	$191.00
Purchase #5	$149.62	8.556%	$162.4215	$162.42	$162.40	$162.40
Purchase #6	$130.97	5.269%	$137.8708	$137.87	$137.85	$137.90
Purchase #7	$77.52	10.277%	$85.4867	$85.49	$85.50	$85.50
7 purchase totals =	$895.80		$971.2459	$971.25	$971.20	$971.30