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	$89.77	6.136%	$95.2783	$95.28	$95.30	$95.30
Purchase #2	$219.43	3.322%	$226.7195	$226.72	$226.70	$226.70
Purchase #3	$116.57	12.811%	$131.5038	$131.50	$131.50	$131.50
Purchase #4	$142.30	12.523%	$160.1202	$160.12	$160.10	$160.10
Purchase #5	$134.49	7.455%	$144.5162	$144.52	$144.50	$144.50
Purchase #6	$54.47	9.377%	$59.5777	$59.58	$59.60	$59.60
Purchase #7	$172.61	4.193%	$179.8475	$179.85	$179.85	$179.80
7 purchase totals =	$929.64		$997.5632	$997.57	$997.55	$997.50