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	$24.42	13.153%	$27.632	$27.63	$27.65	$27.60
Purchase #2	$7.79	11.559%	$8.6904	$8.69	$8.70	$8.70
Purchase #3	$54.91	4.639%	$57.4573	$57.46	$57.45	$57.50
Purchase #4	$164.93	12.208%	$185.0647	$185.06	$185.05	$185.10
Purchase #5	$58.67	8.836%	$63.8541	$63.85	$63.85	$63.90
Purchase #6	$187.69	5.743%	$198.469	$198.47	$198.45	$198.50
Purchase #7	$115.27	10.758%	$127.6707	$127.67	$127.65	$127.70
7 purchase totals =	$613.68		$668.8382	$668.83	$668.80	$669.00