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	$74.72	7.688%	$80.4645	$80.46	$80.45	$80.50
Purchase #2	$95.96	3.104%	$98.9386	$98.94	$98.95	$98.90
Purchase #3	$225.57	10.267%	$248.7293	$248.73	$248.75	$248.70
Purchase #4	$148.66	5.570%	$156.9404	$156.94	$156.95	$156.90
Purchase #5	$172.83	4.613%	$180.8026	$180.80	$180.80	$180.80
Purchase #6	$49.35	7.693%	$53.1465	$53.15	$53.15	$53.10
Purchase #7	$164.76	10.156%	$181.493	$181.49	$181.50	$181.50
7 purchase totals =	$931.85		$1,000.5149	$1,000.51	$1,000.55	$1,000.40