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	$100.93	4.561%	$105.5334	$105.53	$105.55	$105.50
Purchase #2	$246.59	4.760%	$258.3277	$258.33	$258.35	$258.30
Purchase #3	$103.71	5.214%	$109.1174	$109.12	$109.10	$109.10
Purchase #4	$11.73	4.362%	$12.2417	$12.24	$12.25	$12.20
Purchase #5	$9.57	13.320%	$10.8447	$10.84	$10.85	$10.80
Purchase #6	$122.56	9.267%	$133.9176	$133.92	$133.90	$133.90
Purchase #7	$50.80	7.436%	$54.5775	$54.58	$54.60	$54.60
7 purchase totals =	$645.89		$684.5600	$684.56	$684.60	$684.40