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	$240.73	7.805%	$259.519	$259.52	$259.50	$259.50
Purchase #2	$39.91	7.485%	$42.8973	$42.90	$42.90	$42.90
Purchase #3	$200.88	10.728%	$222.4304	$222.43	$222.45	$222.40
Purchase #4	$30.68	7.824%	$33.0804	$33.08	$33.10	$33.10
Purchase #5	$132.69	4.848%	$139.1228	$139.12	$139.10	$139.10
Purchase #6	$11.90	13.140%	$13.4637	$13.46	$13.45	$13.50
Purchase #7	$61.55	8.162%	$66.5737	$66.57	$66.55	$66.60
7 purchase totals =	$718.34		$777.0873	$777.08	$777.05	$777.10