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	$98.34	10.867%	$109.0266	$109.03	$109.05	$109.00
Purchase #2	$40.37	13.106%	$45.6609	$45.66	$45.65	$45.70
Purchase #3	$35.94	4.402%	$37.5221	$37.52	$37.50	$37.50
Purchase #4	$218.99	12.525%	$246.4185	$246.42	$246.40	$246.40
Purchase #5	$120.50	11.252%	$134.0587	$134.06	$134.05	$134.10
Purchase #6	$208.47	13.654%	$236.9345	$236.93	$236.95	$236.90
Purchase #7	$49.30	11.290%	$54.866	$54.87	$54.85	$54.90
7 purchase totals =	$771.91		$864.4873	$864.49	$864.45	$864.50