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	$19.90	9.739%	$21.8381	$21.84	$21.85	$21.80
Purchase #2	$105.87	5.371%	$111.5563	$111.56	$111.55	$111.60
Purchase #3	$111.86	4.469%	$116.859	$116.86	$116.85	$116.90
Purchase #4	$208.50	3.867%	$216.5627	$216.56	$216.55	$216.60
Purchase #5	$14.27	4.192%	$14.8682	$14.87	$14.85	$14.90
Purchase #6	$120.88	13.859%	$137.6328	$137.63	$137.65	$137.60
Purchase #7	$42.39	4.309%	$44.2166	$44.22	$44.20	$44.20
7 purchase totals =	$623.67		$663.5337	$663.54	$663.50	$663.60