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	$173.72	6.506%	$185.0222	$185.02	$185.00	$185.00
Purchase #2	$209.82	4.604%	$219.4801	$219.48	$219.50	$219.50
Purchase #3	$36.45	7.563%	$39.2067	$39.21	$39.20	$39.20
Purchase #4	$34.80	10.437%	$38.4321	$38.43	$38.45	$38.40
Purchase #5	$20.75	3.521%	$21.4806	$21.48	$21.50	$21.50
Purchase #6	$222.29	4.755%	$232.8599	$232.86	$232.85	$232.90
Purchase #7	$224.83	3.856%	$233.4994	$233.50	$233.50	$233.50
7 purchase totals =	$922.66		$969.9810	$969.98	$970.00	$970.00