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	$38.77	3.159%	$39.9947	$39.99	$40.00	$40.00
Purchase #2	$182.72	4.805%	$191.4997	$191.50	$191.50	$191.50
Purchase #3	$108.98	3.227%	$112.4968	$112.50	$112.50	$112.50
Purchase #4	$250.73	12.502%	$282.0763	$282.08	$282.10	$282.10
Purchase #5	$54.83	3.843%	$56.9371	$56.94	$56.95	$56.90
Purchase #6	$122.65	3.847%	$127.3683	$127.37	$127.35	$127.40
Purchase #7	$178.67	4.825%	$187.2908	$187.29	$187.30	$187.30
7 purchase totals =	$937.35		$997.6637	$997.67	$997.70	$997.70