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	$81.40	11.416%	$90.6926	$90.69	$90.70	$90.70
Purchase #2	$61.25	12.580%	$68.9553	$68.96	$68.95	$69.00
Purchase #3	$78.27	5.198%	$82.3385	$82.34	$82.35	$82.30
Purchase #4	$11.55	9.372%	$12.6325	$12.63	$12.65	$12.60
Purchase #5	$113.90	8.203%	$123.2432	$123.24	$123.25	$123.20
Purchase #6	$116.96	5.521%	$123.4174	$123.42	$123.40	$123.40
Purchase #7	$44.28	9.126%	$48.321	$48.32	$48.30	$48.30
7 purchase totals =	$507.61		$549.6005	$549.60	$549.60	$549.50