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	$231.27	9.605%	$253.4835	$253.48	$253.50	$253.50
Purchase #2	$114.73	5.314%	$120.8268	$120.83	$120.85	$120.80
Purchase #3	$95.68	5.195%	$100.6506	$100.65	$100.65	$100.70
Purchase #4	$222.78	3.276%	$230.0783	$230.08	$230.10	$230.10
Purchase #5	$176.68	4.203%	$184.1059	$184.11	$184.10	$184.10
Purchase #6	$37.85	5.758%	$40.0294	$40.03	$40.05	$40.00
Purchase #7	$105.43	4.206%	$109.8644	$109.86	$109.85	$109.90
7 purchase totals =	$984.42		$1,039.0389	$1,039.04	$1,039.10	$1,039.10