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	$38.96	9.822%	$42.7867	$42.79	$42.80	$42.80
Purchase #2	$212.82	9.663%	$233.3848	$233.38	$233.40	$233.40
Purchase #3	$11.71	13.521%	$13.2933	$13.29	$13.30	$13.30
Purchase #4	$217.91	4.302%	$227.2845	$227.28	$227.30	$227.30
Purchase #5	$68.67	8.517%	$74.5186	$74.52	$74.50	$74.50
Purchase #6	$226.54	5.299%	$238.5444	$238.54	$238.55	$238.50
Purchase #7	$72.94	7.579%	$78.4681	$78.47	$78.45	$78.50
7 purchase totals =	$849.55		$908.2804	$908.27	$908.30	$908.30