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	$27.73	12.771%	$31.2714	$31.27	$31.25	$31.30
Purchase #2	$197.80	11.776%	$221.0929	$221.09	$221.10	$221.10
Purchase #3	$5.47	6.525%	$5.8269	$5.83	$5.85	$5.80
Purchase #4	$208.40	4.264%	$217.2862	$217.29	$217.30	$217.30
Purchase #5	$45.78	5.873%	$48.4687	$48.47	$48.45	$48.50
Purchase #6	$232.78	5.617%	$245.8553	$245.86	$245.85	$245.90
Purchase #7	$199.52	4.719%	$208.9353	$208.94	$208.95	$208.90
7 purchase totals =	$917.48		$978.7367	$978.75	$978.75	$978.80