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	$43.37	9.699%	$47.5765	$47.58	$47.60	$47.60
Purchase #2	$39.71	7.361%	$42.6331	$42.63	$42.65	$42.60
Purchase #3	$118.44	4.619%	$123.9107	$123.91	$123.90	$123.90
Purchase #4	$15.37	12.792%	$17.3361	$17.34	$17.35	$17.30
Purchase #5	$40.27	8.168%	$43.5593	$43.56	$43.55	$43.60
Purchase #6	$123.60	6.575%	$131.7267	$131.73	$131.75	$131.70
Purchase #7	$189.54	5.177%	$199.3525	$199.35	$199.35	$199.40
7 purchase totals =	$570.30		$606.0949	$606.10	$606.15	$606.10