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	$16.64	11.401%	$18.5371	$18.54	$18.55	$18.50
Purchase #2	$228.90	3.342%	$236.5498	$236.55	$236.55	$236.50
Purchase #3	$184.63	7.831%	$199.0884	$199.09	$199.10	$199.10
Purchase #4	$81.77	10.407%	$90.2798	$90.28	$90.30	$90.30
Purchase #5	$181.77	13.240%	$205.8363	$205.84	$205.85	$205.80
Purchase #6	$42.85	6.812%	$45.7689	$45.77	$45.75	$45.80
Purchase #7	$107.94	4.373%	$112.6602	$112.66	$112.65	$112.70
7 purchase totals =	$844.50		$908.7205	$908.73	$908.75	$908.70