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	$39.77	6.581%	$42.3873	$42.39	$42.40	$42.40
Purchase #2	$89.85	5.621%	$94.9005	$94.90	$94.90	$94.90
Purchase #3	$29.57	4.827%	$30.9973	$31.00	$31.00	$31.00
Purchase #4	$232.56	10.276%	$256.4579	$256.46	$256.45	$256.50
Purchase #5	$94.92	3.401%	$98.1482	$98.15	$98.15	$98.10
Purchase #6	$136.75	3.193%	$141.1164	$141.12	$141.10	$141.10
Purchase #7	$194.27	12.134%	$217.8427	$217.84	$217.85	$217.80
7 purchase totals =	$817.69		$881.8503	$881.86	$881.85	$881.80