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	$239.51	8.480%	$259.8204	$259.82	$259.80	$259.80
Purchase #2	$103.41	9.687%	$113.4273	$113.43	$113.45	$113.40
Purchase #3	$245.43	4.267%	$255.9025	$255.90	$255.90	$255.90
Purchase #4	$200.65	7.178%	$215.0527	$215.05	$215.05	$215.10
Purchase #5	$70.42	13.536%	$79.9521	$79.95	$79.95	$80.00
Purchase #6	$215.33	11.629%	$240.3707	$240.37	$240.35	$240.40
Purchase #7	$229.70	4.693%	$240.4798	$240.48	$240.50	$240.50
7 purchase totals =	$1,304.45		$1,405.0055	$1,405.00	$1,405.00	$1,405.10