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	$231.78	10.214%	$255.454	$255.45	$255.45	$255.50
Purchase #2	$115.35	12.141%	$129.3546	$129.35	$129.35	$129.40
Purchase #3	$28.80	10.244%	$31.7503	$31.75	$31.75	$31.80
Purchase #4	$150.47	11.863%	$168.3203	$168.32	$168.30	$168.30
Purchase #5	$37.92	13.494%	$43.0369	$43.04	$43.05	$43.00
Purchase #6	$152.97	11.735%	$170.921	$170.92	$170.90	$170.90
Purchase #7	$166.61	7.823%	$179.6439	$179.64	$179.65	$179.60
7 purchase totals =	$883.90		$978.4810	$978.47	$978.45	$978.50