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	$20.62	5.774%	$21.8106	$21.81	$21.80	$21.80
Purchase #2	$232.72	9.630%	$255.1309	$255.13	$255.15	$255.10
Purchase #3	$143.82	7.696%	$154.8884	$154.89	$154.90	$154.90
Purchase #4	$67.90	8.360%	$73.5764	$73.58	$73.60	$73.60
Purchase #5	$128.80	11.782%	$143.9752	$143.98	$144.00	$144.00
Purchase #6	$226.88	10.577%	$250.8771	$250.88	$250.90	$250.90
Purchase #7	$93.94	8.546%	$101.9681	$101.97	$101.95	$102.00
7 purchase totals =	$914.68		$1,002.2267	$1,002.24	$1,002.30	$1,002.30