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	$198.96	11.536%	$221.912	$221.91	$221.90	$221.90
Purchase #2	$78.58	6.817%	$83.9368	$83.94	$83.95	$83.90
Purchase #3	$90.70	8.126%	$98.0703	$98.07	$98.05	$98.10
Purchase #4	$115.61	6.809%	$123.4819	$123.48	$123.50	$123.50
Purchase #5	$30.48	7.137%	$32.6554	$32.66	$32.65	$32.70
Purchase #6	$143.83	5.586%	$151.8643	$151.86	$151.85	$151.90
Purchase #7	$105.65	10.688%	$116.9419	$116.94	$116.95	$116.90
7 purchase totals =	$763.81		$828.8626	$828.86	$828.85	$828.90