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	$76.33	8.680%	$82.9554	$82.96	$82.95	$83.00
Purchase #2	$246.69	13.436%	$279.8353	$279.84	$279.85	$279.80
Purchase #3	$87.70	13.550%	$99.5834	$99.58	$99.60	$99.60
Purchase #4	$184.27	10.590%	$203.7842	$203.78	$203.80	$203.80
Purchase #5	$58.53	9.151%	$63.8861	$63.89	$63.90	$63.90
Purchase #6	$198.46	6.534%	$211.4274	$211.43	$211.45	$211.40
Purchase #7	$127.79	11.490%	$142.4731	$142.47	$142.45	$142.50
7 purchase totals =	$979.77		$1,083.9449	$1,083.95	$1,084.00	$1,084.00