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	$128.50	8.828%	$139.844	$139.84	$139.85	$139.80
Purchase #2	$202.56	3.567%	$209.7853	$209.79	$209.80	$209.80
Purchase #3	$63.67	13.758%	$72.4297	$72.43	$72.45	$72.40
Purchase #4	$79.75	3.595%	$82.617	$82.62	$82.60	$82.60
Purchase #5	$198.92	8.195%	$215.2215	$215.22	$215.20	$215.20
Purchase #6	$161.49	10.269%	$178.0734	$178.07	$178.05	$178.10
Purchase #7	$113.61	6.392%	$120.872	$120.87	$120.85	$120.90
7 purchase totals =	$948.50		$1,018.8429	$1,018.84	$1,018.80	$1,018.80