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	$27.61	11.817%	$30.8727	$30.87	$30.85	$30.90
Purchase #2	$118.39	4.436%	$123.6418	$123.64	$123.65	$123.60
Purchase #3	$140.61	13.500%	$159.5924	$159.59	$159.60	$159.60
Purchase #4	$205.97	10.364%	$227.3167	$227.32	$227.30	$227.30
Purchase #5	$117.54	8.562%	$127.6038	$127.60	$127.60	$127.60
Purchase #6	$124.29	6.288%	$132.1054	$132.11	$132.10	$132.10
Purchase #7	$52.38	5.843%	$55.4406	$55.44	$55.45	$55.40
7 purchase totals =	$786.79		$856.5734	$856.57	$856.55	$856.50