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	$132.98	8.666%	$144.504	$144.50	$144.50	$144.50
Purchase #2	$240.61	4.826%	$252.2218	$252.22	$252.20	$252.20
Purchase #3	$144.86	13.278%	$164.0945	$164.09	$164.10	$164.10
Purchase #4	$34.89	7.455%	$37.491	$37.49	$37.50	$37.50
Purchase #5	$130.71	4.414%	$136.4795	$136.48	$136.50	$136.50
Purchase #6	$12.35	12.461%	$13.8889	$13.89	$13.90	$13.90
Purchase #7	$224.61	6.274%	$238.702	$238.70	$238.70	$238.70
7 purchase totals =	$921.01		$987.3817	$987.37	$987.40	$987.40