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	$136.96	6.278%	$145.5583	$145.56	$145.55	$145.60
Purchase #2	$90.75	11.747%	$101.4104	$101.41	$101.40	$101.40
Purchase #3	$123.79	6.200%	$131.465	$131.47	$131.45	$131.50
Purchase #4	$111.44	13.534%	$126.5223	$126.52	$126.50	$126.50
Purchase #5	$67.35	4.866%	$70.6273	$70.63	$70.65	$70.60
Purchase #6	$194.77	6.741%	$207.8994	$207.90	$207.90	$207.90
Purchase #7	$119.85	13.482%	$136.0082	$136.01	$136.00	$136.00
7 purchase totals =	$844.91		$919.4909	$919.50	$919.45	$919.50