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	$35.94	13.132%	$40.6596	$40.66	$40.65	$40.70
Purchase #2	$241.39	7.631%	$259.8105	$259.81	$259.80	$259.80
Purchase #3	$236.27	6.741%	$252.197	$252.20	$252.20	$252.20
Purchase #4	$84.31	6.172%	$89.5136	$89.51	$89.50	$89.50
Purchase #5	$192.67	10.838%	$213.5516	$213.55	$213.55	$213.60
Purchase #6	$204.86	8.808%	$222.9041	$222.90	$222.90	$222.90
Purchase #7	$249.34	3.598%	$258.3113	$258.31	$258.30	$258.30
7 purchase totals =	$1,244.78		$1,336.9477	$1,336.94	$1,336.90	$1,337.00