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	$80.52	12.759%	$90.7935	$90.79	$90.80	$90.80
Purchase #2	$135.61	3.412%	$140.237	$140.24	$140.25	$140.20
Purchase #3	$123.61	10.493%	$136.5804	$136.58	$136.60	$136.60
Purchase #4	$209.43	4.159%	$218.1402	$218.14	$218.15	$218.10
Purchase #5	$16.88	11.501%	$18.8214	$18.82	$18.80	$18.80
Purchase #6	$126.93	10.685%	$140.4925	$140.49	$140.50	$140.50
Purchase #7	$230.95	10.599%	$255.4284	$255.43	$255.45	$255.40
7 purchase totals =	$923.93		$1,000.4934	$1,000.49	$1,000.55	$1,000.40