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	$19.33	11.369%	$21.5276	$21.53	$21.55	$21.50
Purchase #2	$242.71	5.714%	$256.5784	$256.58	$256.60	$256.60
Purchase #3	$22.88	7.567%	$24.6113	$24.61	$24.60	$24.60
Purchase #4	$113.96	10.550%	$125.9828	$125.98	$126.00	$126.00
Purchase #5	$150.52	3.502%	$155.7912	$155.79	$155.80	$155.80
Purchase #6	$113.65	8.636%	$123.4648	$123.46	$123.45	$123.50
Purchase #7	$143.66	8.805%	$156.3093	$156.31	$156.30	$156.30
7 purchase totals =	$806.71		$864.2654	$864.26	$864.30	$864.30