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	$250.42	6.296%	$266.1864	$266.19	$266.20	$266.20
Purchase #2	$151.75	13.859%	$172.781	$172.78	$172.80	$172.80
Purchase #3	$50.38	3.349%	$52.0672	$52.07	$52.05	$52.10
Purchase #4	$97.30	10.249%	$107.2723	$107.27	$107.25	$107.30
Purchase #5	$40.87	12.282%	$45.8897	$45.89	$45.90	$45.90
Purchase #6	$180.91	3.867%	$187.9058	$187.91	$187.90	$187.90
Purchase #7	$166.79	4.553%	$174.3839	$174.38	$174.40	$174.40
7 purchase totals =	$938.42		$1,006.4863	$1,006.49	$1,006.50	$1,006.60