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	$45.64	11.527%	$50.9009	$50.90	$50.90	$50.90
Purchase #2	$164.67	11.638%	$183.8343	$183.83	$183.85	$183.80
Purchase #3	$184.52	8.473%	$200.1544	$200.15	$200.15	$200.20
Purchase #4	$122.30	11.210%	$136.0098	$136.01	$136.00	$136.00
Purchase #5	$143.77	11.856%	$160.8154	$160.82	$160.80	$160.80
Purchase #6	$238.63	9.373%	$260.9968	$261.00	$261.00	$261.00
Purchase #7	$100.33	4.546%	$104.891	$104.89	$104.90	$104.90
7 purchase totals =	$999.86		$1,097.6026	$1,097.60	$1,097.60	$1,097.60