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	$9.50	13.686%	$10.8002	$10.80	$10.80	$10.80
Purchase #2	$156.26	7.518%	$168.0076	$168.01	$168.00	$168.00
Purchase #3	$211.54	12.429%	$237.8323	$237.83	$237.85	$237.80
Purchase #4	$189.80	11.443%	$211.5188	$211.52	$211.50	$211.50
Purchase #5	$48.37	12.197%	$54.2697	$54.27	$54.25	$54.30
Purchase #6	$213.31	8.673%	$231.8104	$231.81	$231.80	$231.80
Purchase #7	$58.50	9.628%	$64.1324	$64.13	$64.15	$64.10
7 purchase totals =	$887.28		$978.3714	$978.37	$978.35	$978.30