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	$38.27	3.729%	$39.6971	$39.70	$39.70	$39.70
Purchase #2	$235.70	10.228%	$259.8074	$259.81	$259.80	$259.80
Purchase #3	$56.40	5.500%	$59.502	$59.50	$59.50	$59.50
Purchase #4	$120.37	11.400%	$134.0922	$134.09	$134.10	$134.10
Purchase #5	$122.73	11.446%	$136.7777	$136.78	$136.80	$136.80
Purchase #6	$72.92	7.647%	$78.4962	$78.50	$78.50	$78.50
Purchase #7	$80.63	9.272%	$88.106	$88.11	$88.10	$88.10
7 purchase totals =	$727.02		$796.4786	$796.49	$796.50	$796.50