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	$16.41	8.844%	$17.8613	$17.86	$17.85	$17.90
Purchase #2	$6.72	11.266%	$7.4771	$7.48	$7.50	$7.50
Purchase #3	$168.42	7.473%	$181.006	$181.01	$181.00	$181.00
Purchase #4	$21.38	13.863%	$24.3439	$24.34	$24.35	$24.30
Purchase #5	$156.84	6.400%	$166.8778	$166.88	$166.90	$166.90
Purchase #6	$92.83	6.531%	$98.8927	$98.89	$98.90	$98.90
Purchase #7	$135.43	5.715%	$143.1698	$143.17	$143.15	$143.20
7 purchase totals =	$598.03		$639.6286	$639.63	$639.65	$639.70