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	$67.65	4.656%	$70.7998	$70.80	$70.80	$70.80
Purchase #2	$157.83	8.284%	$170.9046	$170.90	$170.90	$170.90
Purchase #3	$157.49	9.611%	$172.6264	$172.63	$172.65	$172.60
Purchase #4	$189.50	3.859%	$196.8128	$196.81	$196.80	$196.80
Purchase #5	$106.34	5.128%	$111.7931	$111.79	$111.80	$111.80
Purchase #6	$183.44	9.538%	$200.9365	$200.94	$200.95	$200.90
Purchase #7	$76.71	7.147%	$82.1925	$82.19	$82.20	$82.20
7 purchase totals =	$938.96		$1,006.0657	$1,006.06	$1,006.10	$1,006.00