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	$197.39	10.552%	$218.2186	$218.22	$218.20	$218.20
Purchase #2	$203.31	10.448%	$224.5518	$224.55	$224.55	$224.60
Purchase #3	$86.89	3.757%	$90.1545	$90.15	$90.15	$90.20
Purchase #4	$30.47	6.579%	$32.4746	$32.47	$32.45	$32.50
Purchase #5	$151.32	8.752%	$164.5635	$164.56	$164.55	$164.60
Purchase #6	$93.99	12.337%	$105.5855	$105.59	$105.60	$105.60
Purchase #7	$6.26	4.409%	$6.536	$6.54	$6.55	$6.50
7 purchase totals =	$769.63		$842.0845	$842.08	$842.05	$842.20