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	$237.67	7.683%	$255.9302	$255.93	$255.95	$255.90
Purchase #2	$70.30	10.673%	$77.8031	$77.80	$77.80	$77.80
Purchase #3	$116.88	12.389%	$131.3603	$131.36	$131.35	$131.40
Purchase #4	$50.94	10.248%	$56.1603	$56.16	$56.15	$56.20
Purchase #5	$199.82	12.427%	$224.6516	$224.65	$224.65	$224.70
Purchase #6	$36.57	8.162%	$39.5548	$39.55	$39.55	$39.60
Purchase #7	$42.38	3.540%	$43.8803	$43.88	$43.90	$43.90
7 purchase totals =	$754.56		$829.3406	$829.33	$829.35	$829.50