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	$37.42	13.447%	$42.4519	$42.45	$42.45	$42.50
Purchase #2	$132.92	11.688%	$148.4557	$148.46	$148.45	$148.50
Purchase #3	$241.49	11.466%	$269.1792	$269.18	$269.20	$269.20
Purchase #4	$210.62	11.750%	$235.3679	$235.37	$235.35	$235.40
Purchase #5	$137.68	10.177%	$151.6917	$151.69	$151.70	$151.70
Purchase #6	$30.37	5.860%	$32.1497	$32.15	$32.15	$32.10
Purchase #7	$61.39	11.166%	$68.2448	$68.24	$68.25	$68.20
7 purchase totals =	$851.89		$947.5409	$947.54	$947.55	$947.60