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	$127.92	12.517%	$143.9317	$143.93	$143.95	$143.90
Purchase #2	$190.39	6.265%	$202.3179	$202.32	$202.30	$202.30
Purchase #3	$76.51	8.374%	$82.9169	$82.92	$82.90	$82.90
Purchase #4	$9.51	8.359%	$10.3049	$10.30	$10.30	$10.30
Purchase #5	$187.30	5.768%	$198.1035	$198.10	$198.10	$198.10
Purchase #6	$68.75	13.179%	$77.8106	$77.81	$77.80	$77.80
Purchase #7	$95.43	5.109%	$100.3055	$100.31	$100.30	$100.30
7 purchase totals =	$755.81		$815.6910	$815.69	$815.65	$815.60