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	$34.86	11.548%	$38.8856	$38.89	$38.90	$38.90
Purchase #2	$12.59	10.404%	$13.8999	$13.90	$13.90	$13.90
Purchase #3	$172.85	11.600%	$192.9006	$192.90	$192.90	$192.90
Purchase #4	$218.43	5.201%	$229.7905	$229.79	$229.80	$229.80
Purchase #5	$39.82	9.271%	$43.5117	$43.51	$43.50	$43.50
Purchase #6	$39.82	13.240%	$45.0922	$45.09	$45.10	$45.10
Purchase #7	$197.83	9.673%	$216.9661	$216.97	$216.95	$217.00
7 purchase totals =	$716.20		$781.0466	$781.05	$781.05	$781.10