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	$245.44	8.739%	$266.889	$266.89	$266.90	$266.90
Purchase #2	$219.89	4.104%	$228.9143	$228.91	$228.90	$228.90
Purchase #3	$137.65	4.201%	$143.4327	$143.43	$143.45	$143.40
Purchase #4	$173.61	5.633%	$183.3895	$183.39	$183.40	$183.40
Purchase #5	$201.85	13.197%	$228.4881	$228.49	$228.50	$228.50
Purchase #6	$81.86	9.850%	$89.9232	$89.92	$89.90	$89.90
Purchase #7	$29.63	4.564%	$30.9823	$30.98	$31.00	$31.00
7 purchase totals =	$1,089.93		$1,172.0191	$1,172.01	$1,172.05	$1,172.00