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	$79.66	12.692%	$89.7704	$89.77	$89.75	$89.80
Purchase #2	$108.97	6.874%	$116.4606	$116.46	$116.45	$116.50
Purchase #3	$177.57	3.850%	$184.4064	$184.41	$184.40	$184.40
Purchase #4	$168.93	13.263%	$191.3352	$191.34	$191.35	$191.30
Purchase #5	$196.31	4.425%	$204.9967	$205.00	$205.00	$205.00
Purchase #6	$72.27	8.553%	$78.4513	$78.45	$78.45	$78.50
Purchase #7	$110.82	13.163%	$125.4072	$125.41	$125.40	$125.40
7 purchase totals =	$914.53		$990.8278	$990.84	$990.80	$990.90